C Programming Tutorial PDF

C Programming Tutorial C PROGRAMMING TUTORIAL Simply Easy Learning by tutorialspoint.com tutorialspoint.com i COPYRIGHT & DISCLAIMER NOTICE  All the content and graphics on this tutorial are the property of tutorialspoint.com. Any content from tutorialspoint.com or this tutorial may not be redistributed or reproduced in any way, shape, or form without the written permission of tutorialspoint.com. Failure to do so is a violation of copyright laws. This tutorial may contain inaccuracies or errors and tutorialspoint provides no guarantee regarding the accuracy of the site or its contents including this tutorial. If you discover that the tutorialspoint.com site or this tutorial content contains some errors, please contact us at [email protected] ii Table of Contents C Language Overview.............................................................. 1 Facts about C............................................................................................... 1 Why to use C ?............................................................................................. 2 C Programs.................................................................................................. 2 C Environment Setup............................................................... 3 Text Editor................................................................................................... 3 The C Compiler............................................................................................ 3 Installation on Unix/Linux............................................................................. 4 Installation on Mac OS.................................................................................. 4 Installation on Windows............................................................................... 4 C Program Structure................................................................ 5 C Hello World Example................................................................................. 5 Compile & Execute C Program....................................................................... 6 C Basic Syntax......................................................................... 7 Tokens in C.................................................................................................. 7 Semicolons ;................................................................................................ 7 Comments................................................................................................... 8 Identifiers.................................................................................................... 8 Keywords.................................................................................................... 8 Whitespace in C........................................................................................... 9 C Data Types......................................................................... 10 Integer Types............................................................................................. 10 Floating-Point Types................................................................................... 11 The void Type............................................................................................ 12 C Variables............................................................................ 13 Variable Declaration in C................................Error! Bookmark not defined. Variable Initialization in C...............................Error! Bookmark not defined. Lvalues and Rvalues in C............................................................................. 15 C Constants and Literals........................................................ 17 Integer literals............................................................................................ 17 Floating-point literals.................................................................................. 18 Character constants.................................................................................... 18 iii String literals.............................................................................................. 19 Defining Constants..................................................................................... 19 The #define Preprocessor...................................................................... 19 The const Keyword................................................................................. 20 C Storage Classes................................................................. 22 The auto Storage Class................................................................................ 22 The register Storage Class........................................................................... 22 The static Storage Class............................................................................... 23 The extern Storage Class............................................................................. 24 C Operators........................................................................... 25 Arithmetic Operators.................................................................................. 25 Relational Operators................................................................................... 26 Logical Operators....................................................................................... 28 Bitwise Operators....................................................................................... 29 Assignment Operators................................................................................ 31 Misc Operators ↦ sizeof & ternary.............................................................. 33 Operators Precedence in C.......................................................................... 33 Decision Making in C.............................................................. 35 if statement............................................................................................... 36 Syntax..................................................................................................... 36 Flow Diagram.......................................................................................... 36 Example.................................................................................................. 36 if...else statement...................................................................................... 37 Syntax..................................................................................................... 37 Flow Diagram.......................................................................................... 38 Example.................................................................................................. 38 The if...else if...else Statement..................................................................... 39 Syntax..................................................................................................... 39 Example.................................................................................................. 39 Nested if statements.................................................................................. 40 Syntax..................................................................................................... 40 Example.................................................................................................. 40 switch statement....................................................................................... 41 Syntax..................................................................................................... 41 Flow Diagram.......................................................................................... 42 Example.................................................................................................. 42 Nested switch statements........................................................................... 43 Syntax..................................................................................................... 43 Example.................................................................................................. 43 iii The ? : Operator......................................................................................... 44 C Loops.................................................................................. 45 while loop in C........................................................................................... 46 Syntax..................................................................................................... 46 Flow Diagram.......................................................................................... 46 Example.................................................................................................. 47 for loop in C............................................................................................... 47 Syntax..................................................................................................... 47 Flow Diagram.......................................................................................... 48 Example.................................................................................................. 48 do...while loop in C..................................................................................... 49 Syntax..................................................................................................... 49 Flow Diagram.......................................................................................... 50 Example.................................................................................................. 50 nested loops in C........................................................................................ 51 Syntax..................................................................................................... 51 Example.................................................................................................. 52 break statement in C.................................................................................. 53 Syntax..................................................................................................... 53 Flow Diagram.......................................................................................... 53 Example.................................................................................................. 54 continue statement in C.............................................................................. 54 Syntax..................................................................................................... 54 Flow Diagram.......................................................................................... 55 Example.................................................................................................. 55 goto statement in C.................................................................................... 56 Syntax..................................................................................................... 56 Flow Diagram.......................................................................................... 56 Example.................................................................................................. 57 The Infinite Loop........................................................................................ 57 C Functions............................................................................ 59 Defining a Function.................................................................................... 59 Example.................................................................................................. 60 Function Declarations................................................................................. 60 Calling a Function....................................................................................... 60 Function Arguments................................................................................... 61 Function call by value............................................................................. 62 Function call by reference....................................................................... 63 C Scope Rules....................................................................... 65 iii Local Variables........................................................................................... 65 Global Variables......................................................................................... 66 Formal Parameters..................................................................................... 67 Initializing Local and Global Variables........................................................... 67 C Arrays................................................................................. 69 Declaring Arrays......................................................................................... 69 Initializing Arrays........................................................................................ 70 Accessing Array Elements............................................................................ 70 Multi-dimensional Arrays............................................................................ 71 Two-Dimensional Arrays............................................................................. 71 Initializing Two-Dimensional Arrays.............................................................. 72 Accessing Two-Dimensional Array Elements................................................. 72 Passing Arrays as Function Arguments.......................................................... 73 Way-1...................................................................................................... 73 Way-2...................................................................................................... 74 Way-3....................................................................................................... 74 Example.................................................................................................. 74 Return array from function.......................................................................... 75 Pointer to an Array..................................................................................... 77 C Pointers.............................................................................. 79 What Are Pointers?.................................................................................... 80 How to use Pointers?.................................................................................. 80 NULL Pointers in C...................................................................................... 81 Pointer arithmetic...................................................................................... 81 Incrementing a Pointer............................................................................... 82 Decrementing a Pointer.............................................................................. 83 Pointer Comparisons.................................................................................. 83 Array of pointers........................................................................................ 84 Pointer to Pointer....................................................................................... 86 Passing pointers to functions....................................................................... 87 Return pointer from functions..................................................................... 88 C Strings................................................................................ 91 C Structures........................................................................... 94 Defining a Structure.................................................................................... 94 Accessing Structure Members..................................................................... 95 Structures as Function Arguments............................................................... 96 Pointers to Structures................................................................................. 97 C Unions.............................................................................. 100 Defining a Union...................................................................................... 100 iii Accessing Union Members........................................................................ 101 Bit Fields.............................................................................. 103 Bit Field Declaration................................................................................. 104 Typedef................................................................................ 106 typedef vs #define.................................................................................... 107 Input & Output...................................................................... 108 The Standard Files.................................................................................... 108 The getchar() & putchar() functions........................................................... 108 The gets() & puts() functions..................................................................... 109 The scanf() and printf() functions............................................................... 110 File I/O................................................................................. 111 Opening Files........................................................................................... 111 Closing a File............................................................................................ 112 Writing a File........................................................................................... 112 Reading a File........................................................................................... 113 Binary I/O Functions................................................................................. 114 Preprocessors...................................................................... 115 Preprocessors Examples............................................................................ 115 Predefined Macros................................................................................... 116 Preprocessor Operators............................................................................ 117 Macro Continuation (\).......................................................................... 117 Stringize (#)........................................................................................... 117 Token Pasting (##)................................................................................ 118 The defined() Operator......................................................................... 118 Parameterized Macros.............................................................................. 119 Header Files......................................................................... 120 Include Syntax.......................................................................................... 120 Include Operation.................................................................................... 121 Once-Only Headers.................................................................................. 121 Computed Includes................................................................................... 122 Type Casting........................................................................ 123 Integer Promotion.................................................................................... 124 Usual Arithmetic Conversion..................................................................... 124 Error Handling...................................................................... 126 The errno, perror() and strerror()............................................................... 126 Divide by zero errors................................................................................ 127 Program Exit Status.................................................................................. 128 Recursion............................................................................. 129 Number Factorial..................................................................................... 129 iii Fibonacci Series....................................................................................... 130 Variable Arguments.............................................................. 131 Memory Management.......................................................... 133 Allocating Memory Dynamically................................................................. 133 Resizing and Releasing Memory................................................................. 134 Command Line Arguments................................................... 136 iii 1 CHAPTER C Language Overview This chapter describes the basic details about C programming language, how it emerged, what are strengths of C and why we should use C. T he C programming language is a general-purpose, high-level language that was originally developed by Dennis M. Ritchie to develop the UNIX operating system at Bell Labs. C was originally first implemented on the DEC PDP-11 computer in 1972. In 1978, Brian Kernighan and Dennis Ritchie produced the first publicly available description of C, now known as the K&R standard. The UNIX operating system, the C compiler, and essentially all UNIX applications programs have been written in C. The C has now become a widely used professional language for various reasons.  Easy to learn  Structured language  It produces efficient programs.  It can handle low-level activities.  It can be compiled on a variety of computer platforms. Facts about C  C was invented to write an operating system called UNIX.  C is a successor of B language, which was introduced around 1970.  The language was formalized in 1988 by the American National Standard Institute. (ANSI).  The UNIX OS was totally written in C by 1973. TUTORIALS POINT Simply Easy Learning Page 1  Today, C is the most widely used and popular System Programming Language.  Most of the state-of-the-art softwares have been implemented using C.  Today's most ][popular Linux OS and RBDMS MySQL have been written in C. Why to use C? C was initially used for system development work, in particular the programs that make up the operating system. C was adopted as a system development language because it produces code that runs nearly as fast as code written in assembly language. Some examples of the use of C might be:  Operating Systems  Language Compilers  Assemblers  Text Editors  Print Spoolers  Network Drivers  Modern Programs  Databases  Language Interpreters  Utilities C Programs A C program can vary from 3 lines to millions of lines and it should be written into one or more text files with extension ".c"; for example, hello.c. You can use "vi", "vim" or any other text editor to write your C program into a file. This tutorial assumes that you know how to edit a text file and how to write source code using any programming language. TUTORIALS POINT Simply Easy Learning Page 2 2 CHAPTER C Environment Setup This section describes how to set up your system environment before you start doing your programming using C language. Before you start doing programming using C programming language, you need the following two softwares available on your computer, (a) Text Editor and (b) The C Compiler. Text Editor This will be used to type your program. Examples of few editors include Windows Notepad, OS Edit command, Brief, Epsilon, EMACS, and vim or vi. Name and version of text editor can vary on different operating systems. For example, Notepad will be used on Windows, and vim or vi can be used on windows as well as Linux or UNIX. The files you create with your editor are called source files and contain program source code. The source files for C programs are typically named with the extension “.c”. Before starting your programming, make sure you have one text editor in place and you have enough experience to write a computer program, save it in a file, compile it and finally execute it. The C Compiler The source code written in source file is the human readable source for your program. It needs to be "compiled", to turn into machine language so that your CPU can actually execute the program as per instructions given. This C programming language compiler will be used to compile your source code into final executable program. I assume you have basic knowledge about a programming language compiler. Most frequently used and free available compiler is GNU C/C++ compiler, otherwise you can have compilers either from HP or Solaris if you have respective Operating Systems. Following section guides you on how to install GNU C/C++ compiler on various OS. I'm mentioning C/C++ together because GNU gcc compiler works for both C and C++ programming languages. TUTORIALS POINT Simply Easy Learning Page 3 Installation on UNIX/Linux If you are using Linux or UNIX, then check whether GCC is installed on your system by entering the following command from the command line: $ gcc -v If you have GNU compiler installed on your machine, then it should print a message something as follows: Using built-in specs. Target: i386-redhat-linux Configured with:../configure --prefix=/usr....... Thread model: posix gcc version 4.1.2 20080704 (Red Hat 4.1.2-46) If GCC is not installed, then you will have to install it yourself using the detailed instructions available athttp://gcc.gnu.org/install/ This tutorial has been written based on Linux and all the given examples have been compiled on Cent OS flavor of Linux system. Installation on Mac OS If you use Mac OS X, the easiest way to obtain GCC is to download the Xcode development environment from Apple's web site and follow the simple installation instructions. Once you have Xcode setup, you will be able to use GNU compiler for C/C++. Xcode is currently available at developer.apple.com/technologies/tools/. Installation on Windows To install GCC at Windows you need to install MinGW. To install MinGW, go to the MinGW homepage, www.mingw.org, and follow the link to the MinGW download page. Download the latest version of the MinGW installation program, which should be named MinGW-.exe. While installing MinWG, at a minimum, you must install gcc-core, gcc-g++, binutils, and the MinGW runtime, but you may wish to install more. Add the bin subdirectory of your MinGW installation to your PATH environment variable, so that you can specify these tools on the command line by their simple names. When the installation is complete, you will be able to run gcc, g++, ar, ranlib, dlltool, and several other GNU tools from the Windows command line. TUTORIALS POINT Simply Easy Learning Page 4 3 CHAPTER C Program Structure Let’s look into Hello World example using C Programming Language. B efore we study basic building blocks of the C programming language, let us look a bare minimum C program structure so that we can take it as a reference in upcoming chapters. C Hello World Example A C program basically consists of the following parts:  Preprocessor Commands  Functions  Variables  Statements & Expressions  Comments Let us look at a simple code that would print the words "Hello World": #include int main() { printf("Hello, World! \n"); return 0; } Let us look various parts of the above program: TUTORIALS POINT Simply Easy Learning Page 5 1. The first line of the program #include is a preprocessor command, which tells a C compiler to include stdio.h file before going to actual compilation. 2. The next line int main() is the main function where program execution begins. 3. The next line will be ignored by the compiler and it has been put to add additional comments in the program. So such lines are called comments in the program. 4. The next line printf(...) is another function available in C which causes the message "Hello, World!" to be displayed on the screen. 5. The next line return 0; terminates main()function and returns the value 0. Compile & Execute C Program Let’s look at how to save the source code in a file, and how to compile and run it. Following are the simple steps: 1. Open a text editor and add the above-mentioned code. 2. Save the file as hello.c 3. Open a command prompt and go to the directory where you saved the file. 4. Type gcc hello.c and press enter to compile your code. 5. If there are no errors in your code, the command prompt will take you to the next line and would generate a.out executable file. 6. Now, type a.out to execute your program. 7. You will be able to see "Hello World" printed on the screen $ gcc hello.c $./a.out Hello, World! Make sure that gcc compiler is in your path and that you are running it in the directory containing source file hello.c. TUTORIALS POINT Simply Easy Learning Page 6 4 CHAPTER C Basic Syntax This chapter will give details about all the basic syntax about C programming language including tokens, keywords, identifiers, etc. Y ou have seen a basic structure of C program, so it will be easy to understand other basic building blocks of the C programming language. Tokens in C A C program consists of various tokens and a token is either a keyword, an identifier, a constant, a string literal, or a symbol. For example, the following C statement consists of five tokens: printf("Hello, World! \n"); The individual tokens are: printf ( "Hello, World! \n" ) ; Semicolons ; In C program, the semicolon is a statement terminator. That is, each individual statement must be ended with a semicolon. It indicates the end of one logical entity. For example, following are two different statements: printf("Hello, World! \n"); return 0; TUTORIALS POINT Simply Easy Learning Page 7 Comments Comments are like helping text in your C program and they are ignored by the compiler. They start with as shown below: You cannot have comments within comments and they do not occur within a string or character literals. Identifiers A C identifier is a name used to identify a variable, function, or any other user-defined item. An identifier starts with a letter A to Z or a to z or an underscore _ followed by zero or more letters, underscores, and digits (0 to 9). C does not allow punctuation characters such as @, $, and % within identifiers. C is a case sensitive programming language. Thus, Manpower and manpower are two different identifiers in C. Here are some examples of acceptable identifiers: mohd zara abc move_name a_123 myname50 _temp j a23b9 retVal Keywords The following list shows the reserved words in C. These reserved words may not be used as constant or variable or any other identifier names. auto else Long switch break enum register typedef case extern return union char float short unsigned const for signed void continue goto sizeof volatile default if static while do int struct _packed double TUTORIALS POINT Simply Easy Learning Page 8 Whitespace in C A line containing only whitespace, possibly with a comment, is known as a blank line, and a C compiler totally ignores it. Whitespace is the term used in C to describe blanks, tabs, newline characters and comments. Whitespace separates one part of a statement from another and enables the compiler to identify where one element in a statement, such as int, ends and the next element begins. Therefore, in the following statement: int age; There must be at least one whitespace character (usually a space) between int and age for the compiler to be able to distinguish them. On the other hand, in the following statement: fruit = apples + oranges; // get the total fruit No whitespace characters are necessary between fruit and =, or between = and apples, although you are free to include some if you wish for readability purpose. TUTORIALS POINT Simply Easy Learning Page 9 5 CHAPTER C Data Types I n the C programming language, data types refer to an extensive system used for declaring variables or functions of different types. The type of a variable determines how much space it occupies in storage and how the bit pattern stored is interpreted. The types in C can be classified as follows: S.N. Types and Description Basic Types: 1 They are arithmetic types and consists of the two types: (a) integer types and (b) floating- point types. Enumerated types: 2 They are again arithmetic types and they are used to define variables that can only be assigned certain discrete integer values throughout the program. The type void: 3 The type specifier void indicates that no value is available. Derived types: 4 They include (a) Pointer types, (b) Array types, (c) Structure types, (d) Union types and (e) Function types. The array types and structure types are referred to collectively as the aggregate types. The type of a function specifies the type of the function's return value. We will see basic types in the following section, whereas, other types will be covered in the upcoming chapters. Integer Types Following table gives you details about standard integer types with its storage sizes and value ranges: Type Storage size Value range Char 1 byte -128 to 127 or 0 to 255 unsigned char 1 byte 0 to 255 TUTORIALS POINT Simply Easy Learning Page 10 signed char 1 byte -128 to 127 Int 2 or 4 bytes -32,768 to 32,767 or -2,147,483,648 to 2,147,483,647 unsigned int 2 or 4 bytes 0 to 65,535 or 0 to 4,294,967,295 Short 2 bytes -32,768 to 32,767 unsigned short 2 bytes 0 to 65,535 Long 4 bytes -2,147,483,648 to 2,147,483,647 unsigned long 4 bytes 0 to 4,294,967,295 To get the exact size of a type or a variable on a particular platform, you can use the sizeof operator. The expressions sizeof(type) yields the storage size of the object or type in bytes. Following is an example to get the size of int type on any machine: #include #include int main() { printf("Storage size for int : %d \n", sizeof(int)); return 0; } When you compile and execute the above program, it produces the following result on Linux: Storage size for int : 4 Floating-Point Types Following table gives you details about standard floating-point types with storage sizes and value ranges and their precision: Type Storage size Value range Precision float 4 byte 1.2E-38 to 3.4E+38 6 decimal places double 8 byte 2.3E-308 to 1.7E+308 15 decimal places long double 10 byte 3.4E-4932 to 1.1E+4932 19 decimal places The header file float.h defines macros that allow you to use these values and other details about the binary representation of real numbers in your programs. Following example will print storage space taken by a float type and its range values: #include #include int main() TUTORIALS POINT Simply Easy Learning Page 11 { printf("Storage size for float : %d \n", sizeof(float)); printf("Minimum float positive value: %E\n", FLT_MIN ); printf("Maximum float positive value: %E\n", FLT_MAX ); printf("Precision value: %d\n", FLT_DIG ); return 0; } When you compile and execute the above program, it produces the following result on Linux: Storage size for float : 4 Minimum float positive value: 1.175494E-38 Maximum float positive value: 3.402823E+38 Precision value: 6 The void Type The void type specifies that no value is available. It is used in three kinds of situations: S.N. Types and Description Function returns as void There are various functions in C which do not return value or you can say they return void. 1 A function with no return value has the return type as void. For example, void exit (int status); Function arguments as void 2 There are various functions in C which do not accept any parameter. A function with no parameter can accept as a void. For example, int rand(void); Pointers to void A pointer of type void * represents the address of an object, but not its type. For example, 3 a memory allocation function void *malloc( size_t size ); returns a pointer to void which can be casted to any data type. The void type may not be understood to you at this point, so let us proceed and we will cover these concepts in the upcoming chapters. TUTORIALS POINT Simply Easy Learning Page 12 6 CHAPTER C Variables A variable is nothing but a name given to a storage area that our programs can manipulate. Each variable in C has a specific type, which determines the size and layout of the variable's memory; the range of values that can be stored within that memory; and the set of operations that can be applied to the variable. The name of a variable can be composed of letters, digits, and the underscore character. It must begin with either a letter or an underscore. Upper and lowercase letters are distinct because C is case-sensitive. Based on the basic types explained in previous chapter, there will be the following basic variable types: Type Description Char Typically a single octet(one byte). This is an integer type. Int The most natural size of integer for the machine. Float A single-precision floating point value. Double A double-precision floating point value. Void Represents the absence of type. C programming language also allows to define various other types of variables, which we will cover in subsequent chapters like Enumeration, Pointer, Array, Structure, Union, etc. For this chapter, let us study only basic variable types. Variable Definition in C: A variable definition means to tell the compiler where and how much to create the storage for the variable. A variable definition specifies a data type and contains a list of one or more variables of that type as follows: type variable_list; Here, type must be a valid C data type including char, w_char, int, float, double, bool or any user- defined object, etc., and variable_list may consist of one or more identifier names separated by commas. Some valid declarations are shown here: TUTORIALS POINT Simply Easy Learning Page 13 int i, j, k; char c, ch; float f, salary; double d; The line int i, j, k; both declares and defines the variables i, j and k; which instructs the compiler to create variables named i, j and k of type int. Variables can be initialized (assigned an initial value) in their declaration. The initializer consists of an equal sign followed by a constant expression as follows: type variable_name = value; Some examples are: extern int d = 3, f = 5; // declaration of d and f. int d = 3, f = 5; // definition and initializing d and f. byte z = 22; // definition and initializes z. char x = 'x'; // the variable x has the value 'x'. For definition without an initializer: variables with static storage duration are implicitly initialized with NULL (all bytes have the value 0); the initial value of all other variables is undefined. Variable Declaration in C: A variable declaration provides assurance to the compiler that there is one variable existing with the given type and name so that compiler proceed for further compilation without needing complete detail about the variable. A variable declaration has its meaning at the time of compilation only, compiler needs actual variable declaration at the time of linking of the program. A variable declaration is useful when you are using multiple files and you define your variable in one of the files, which will be available at the time of linking of the program. You will use extern keyword to declare a variable at any place. Though you can declare a variable multiple times in your C program but it can be defined only once in a file, a function or a block of code. Example Try the following example, where variables have been declared at the top, but they have been defined and initialized inside the main function: #include // Variable definition: extern int a, b; extern int c; extern float f; int main () { // Variable definition: int a, b; int c; float f; // actual initialization a =10; TUTORIALS POINT Simply Easy Learning Page 14 b =20; c = a + b; printf("value of c : %d \n", c); f = 70.0/3.0; printf("value of f : %f \n", f); return 0; } When the above code is compiled and executed, it produces the following result: value of c : 30 value of f : 23.333334 Same concept applies on function declaration where you provide a function name at the time of its declaration and its actual definition can be given anywhere else. For example: // function declaration int func(); int main() { // function call int i = func(); } // function definition int func() { return 0; } Lvalues and Rvalues in C There are two kinds of expressions in C: 1. lvalue: An expression that is an lvalue may appear as either the left-hand or right-hand side of an assignment. 2. rvalue: An expression that is an rvalue may appear on the right- but not left-hand side of an assignment. Variables are lvalues and so may appear on the left-hand side of an assignment. Numeric literals are rvalues and so may not be assigned and cannot appear on the left-hand side. Following is a valid statement: int g = 20; But following is not a valid statement and would generate compile-time error: TUTORIALS POINT Simply Easy Learning Page 15 10 = 20; TUTORIALS POINT Simply Easy Learning Page 16 7 CHAPTER C Constants and Literals T he constants refer to fixed values that the program may not alter during its execution. These fixed values are also called literals. Constants can be of any of the basic data types like an integer constant, a floating constant, a character constant, or a string literal. There are also enumeration constants as well. The constants are treated just like regular variables except that their values cannot be modified after their definition. Integer literals An integer literal can be a decimal, octal, or hexadecimal constant. A prefix specifies the base or radix: 0x or 0X for hexadecimal, 0 for octal, and nothing for decimal. An integer literal can also have a suffix that is a combination of U and L, for unsigned and long, respectively. The suffix can be uppercase or lowercase and can be in any order. Here are some examples of integer literals: 212 215u 0xFeeL 078 032UU Following are other examples of various types of Integer literals: 85 0213 0x4b 30 30u 30l 30ul TUTORIALS POINT Simply Easy Learning Page 17 Floating-point literals A floating-point literal has an integer part, a decimal point, a fractional part, and an exponent part. You can represent floating point literals either in decimal form or exponential form. While representing using decimal form, you must include the decimal point, the exponent, or both and while representing using exponential form, you must include the integer part, the fractional part, or both. The signed exponent is introduced by e or E. Here are some examples of floating-point literals: 3.14159 314159E-5L 510E 210f.e55 Character constants Character literals are enclosed in single quotes, e.g., 'x' and can be stored in a simple variable of char type. A character literal can be a plain character (e.g., 'x'), an escape sequence (e.g., '\t'), or a universal character (e.g., '\u02C0'). There are certain characters in C when they are preceded by a backslash they will have special meaning and they are used to represent like newline (\n) or tab (\t). Here, you have a list of some of such escape sequence codes: Escape Meaning sequence \\ \ character \' ' character \" " character \? ? character \a Alert or bell \b Backspace \f Form feed \n Newline \r Carriage return \t Horizontal tab \v Vertical tab \ooo Octal number of one to three digits TUTORIALS POINT Simply Easy Learning Page 18 \xhh... Hexadecimal number of one or more digits Following is the example to show few escape sequence characters: #include int main() { printf("Hello\tWorld\n\n"); return 0; } When the above code is compiled and executed, it produces the following result: Hello World String literals String literals or constants are enclosed in double quotes "". A string contains characters that are similar to character literals: plain characters, escape sequences, and universal characters. You can break a long line into multiple lines using string literals and separating them using whitespaces. Here are some examples of string literals. All the three forms are identical strings. "hello, dear" "hello, \ dear" "hello, " "d" "ear" Defining Constants There are two simple ways in C to define constants: 1. Using #define preprocessor. 2. Using const keyword. The #define Preprocessor Following is the form to use #define preprocessor to define a constant: TUTORIALS POINT Simply Easy Learning Page 19 #define identifier value Following example explains it in detail: #include #define LENGTH 10 #define WIDTH 5 #define NEWLINE '\n' int main() { int area; area = LENGTH * WIDTH; printf("value of area : %d", area); printf("%c", NEWLINE); return 0; } When the above code is compiled and executed, it produces the following result: value of area : 50 The const Keyword You can use const prefix to declare constants with a specific type as follows: const type variable = value; Following example explains it in detail: #include int main() { const int LENGTH = 10; const int WIDTH = 5; const char NEWLINE = '\n'; int area; area = LENGTH * WIDTH; printf("value of area : %d", area); printf("%c", NEWLINE); return 0; } When the above code is compiled and executed, it produces the following result: TUTORIALS POINT Simply Easy Learning Page 20 value of area : 50 Note that it is a good programming practice to define constants in CAPITALS. TUTORIALS POINT Simply Easy Learning Page 21 8 CHAPTER C Storage Classes A storage class defines the scope (visibility) and life-time of variables and/or functions within a C Program. These specifiers precede the type that they modify. There are the following storage classes, which can be used in a C Program  auto  register  static  extern The auto Storage Class The auto storage class is the default storage class for all local variables. { int mount; auto int month; } The example above defines two variables with the same storage class, auto can only be used within functions, i.e., local variables. The register Storage Class The register storage class is used to define local variables that should be stored in a register instead of RAM. This means that the variable has a maximum size equal to the register size (usually one word) and can't have the unary '&' operator applied to it (as it does not have a memory location). { register int miles; } TUTORIALS POINT Simply Easy Learning Page 22 The register should only be used for variables that require quick access such as counters. It should also be noted that defining 'register' does not mean that the variable will be stored in a register. It means that it MIGHT be stored in a register depending on hardware and implementation restrictions. The static Storage Class The static storage class instructs the compiler to keep a local variable in existence during the life-time of the program instead of creating and destroying it each time it comes into and goes out of scope. Therefore, making local variables static allows them to maintain their values between function calls. The static modifier may also be applied to global variables. When this is done, it causes that variable's scope to be restricted to the file in which it is declared. In C programming, when static is used on a class data member, it causes only one copy of that member to be shared by all objects of its class. #include void func(void); static int count = 5; main() { while(count--) { func(); } return 0; } void func( void ) { static int i = 5; i++; printf("i is %d and count is %d\n", i, count); } You may not understand this example at this time because I have used function and global variables, which I have not explained so far. So for now, let us proceed even if you do not understand it completely. When the above code is compiled and executed, it produces the following result: i is 6 and count is 4 i is 7 and count is 3 i is 8 and count is 2 i is 9 and count is 1 i is 10 and count is 0 TUTORIALS POINT Simply Easy Learning Page 23 The extern Storage Class The extern storage class is used to give a reference of a global variable that is visible to ALL the program files. When you use 'extern', the variable cannot be initialized as all it does is point the variable name at a storage location that has been previously defined. When you have multiple files and you define a global variable or function, which will be used in other files also, then extern will be used in another file to give reference of defined variable or function. Just for understanding, extern is used to declare a global variable or function in another file. The extern modifier is most commonly used when there are two or more files sharing the same global variables or functions as explained below. First File: main.c #include int count ; extern void write_extern(); main() { write_extern(); } Second File: write.c #include extern int count; void write_extern(void) { count = 5; printf("count is %d\n", count); } Here, extern keyword is being used to declare count in the second file where as it has its definition in the first file, main.c. Now, compile these two files as follows: $gcc main.c write.c This will produce a.out executable program, when this program is executed, it produces the following result: 5 TUTORIALS POINT Simply Easy Learning Page 24 9 CHAPTER C Operators A n operator is a symbol that tells the compiler to perform specific mathematical or logical manipulations. C language is rich in built-in operators and provides the following types of operators:  Arithmetic Operators  Relational Operators  Logical Operators  Bitwise Operators  Assignment Operators  Misc Operators This tutorial will explain the arithmetic, relational, logical, bitwise, assignment and other operators one by one. Arithmetic Operators Following table shows all the arithmetic operators supported by C language. Assume variable A holds 10 and variable B holds 20, then: Operator Description Example + Adds two operands A + B will give 30 - Subtracts second operand from the first A - B will give -10 * Multiplies both operands A * B will give 200 / Divides numerator by de-numerator B / A will give 2 % Modulus Operator and remainder of after an integer division B % A will give 0 TUTORIALS POINT Simply Easy Learning Page 25 ++ Increments operator increases integer value by one A++ will give 11 -- Decrements operator decreases integer value by one A-- will give 9 Try the following example to understand all the arithmetic operators available in C programming language: #include main() { int a = 21; int b = 10; int c ; c = a + b; printf("Line 1 - Value of c is %d\n", c ); c = a - b; printf("Line 2 - Value of c is %d\n", c ); c = a * b; printf("Line 3 - Value of c is %d\n", c ); c = a / b; printf("Line 4 - Value of c is %d\n", c ); c = a % b; printf("Line 5 - Value of c is %d\n", c ); c = a++; printf("Line 6 - Value of c is %d\n", c ); c = a--; printf("Line 7 - Value of c is %d\n", c ); } When you compile and execute the above program, it produces the following result: Line 1 - Value of c is 31 Line 2 - Value of c is 11 Line 3 - Value of c is 210 Line 4 - Value of c is 2 Line 5 - Value of c is 1 Line 6 - Value of c is 21 Line 7 - Value of c is 22 Relational Operators Following table shows all the relational operators supported by C language. Assume variable A holds 10 and variable B holds 20, then: Operator Description Example TUTORIALS POINT Simply Easy Learning Page 26 Checks if the values of two operands are equal or not, if == (A == B) is not true. yes then condition becomes true. Checks if the values of two operands are equal or not, if != (A != B) is true. values are not equal then condition becomes true. Checks if the value of left operand is greater than the > value of right operand, if yes then condition becomes (A > B) is not true. true. Checks if the value of left operand is less than the value < (A < B) is true. of right operand, if yes then condition becomes true. Checks if the value of left operand is greater than or >= equal to the value of right operand, if yes then condition (A >= B) is not true. becomes true. Checks if the value of left operand is less than or equal > 2 will give 15, which is 0000 1111 number of bits specified by the right operand. Try the following example to understand all the bitwise operators available in C programming language: #include main() { unsigned int a = 60; unsigned int b = 13; int c = 0; c = a & b; printf("Line 1 - Value of c is %d\n", c ); c = a | b; printf("Line 2 - Value of c is %d\n", c ); c = a ^ b; printf("Line 3 - Value of c is %d\n", c ); c = ~a; printf("Line 4 - Value of c is %d\n", c ); c = a > 2; TUTORIALS POINT Simply Easy Learning Page 30 printf("Line 6 - Value of c is %d\n", c ); } When you compile and execute the above program, it produces the following result: Line 1 - Value of c is 12 Line 2 - Value of c is 61 Line 3 - Value of c is 49 Line 4 - Value of c is -61 Line 5 - Value of c is 240 Line 6 - Value of c is 15 Assignment Operators There are following assignment operators supported by C language: Operator Description Example Simple assignment operator, Assigns values C = A + B will assign value of A + = from right side operands to left side operand B into C Add AND assignment operator, It adds right += operand to the left operand and assign the result C += A is equivalent to C = C + A to left operand Subtract AND assignment operator, It subtracts -= right operand from the left operand and assign C -= A is equivalent to C = C - A the result to left operand Multiply AND assignment operator, It multiplies *= right operand with the left operand and assign C *= A is equivalent to C = C * A the result to left operand Divide AND assignment operator, It divides left /= operand with the right operand and assign the C /= A is equivalent to C = C / A result to left operand Modulus AND assignment operator, It takes %= modulus using two operands and assign the C %= A is equivalent to C = C % A result to left operand > 2 &= Bitwise AND assignment operator C &= 2 is same as C = C & 2 ^= bitwise exclusive OR and assignment operator C ^= 2 is same as C = C ^ 2 |= bitwise inclusive OR and assignment operator C |= 2 is same as C = C | 2 Try the following example to understand all the assignment operators available in C programming language: TUTORIALS POINT Simply Easy Learning Page 31 #include main() { int a = 21; int c ; c = a; printf("Line 1 - = Operator Example, Value of c = %d\n", c ); c += a; printf("Line 2 - += Operator Example, Value of c = %d\n", c ); c -= a; printf("Line 3 - -= Operator Example, Value of c = %d\n", c ); c *= a; printf("Line 4 - *= Operator Example, Value of c = %d\n", c ); c /= a; printf("Line 5 - /= Operator Example, Value of c = %d\n", c ); c = 200; c %= a; printf("Line 6 - %= Operator Example, Value of c = %d\n", c ); c = 2; printf("Line 8 - >>= Operator Example, Value of c = %d\n", c ); c &= 2; printf("Line 9 - &= Operator Example, Value of c = %d\n", c ); c ^= 2; printf("Line 10 - ^= Operator Example, Value of c = %d\n", c ); c |= 2; printf("Line 11 - |= Operator Example, Value of c = %d\n", c ); } When you compile and execute the above program, it produces the following result: Line 1 - = Operator Example, Value of c = 21 Line 2 - += Operator Example, Value of c = 42 Line 3 - -= Operator Example, Value of c = 21 Line 4 - *= Operator Example, Value of c = 441 Line 5 - /= Operator Example, Value of c = 21 Line 6 - %= Operator Example, Value of c = 11 Line 7 - = Operator Example, Value of c = 11 TUTORIALS POINT Simply Easy Learning Page 32 Line 9 - &= Operator Example, Value of c = 2 Line 10 - ^= Operator Example, Value of c = 0 Line 11 - |= Operator Example, Value of c = 2 Misc Operators ↦sizeof & ternary There are few other important operators including sizeof and ? : supported by C Language. Operator Description Example sizeof(a), where a is integer, sizeof() Returns the size of an variable. will return 4. &a; will give actual address of & Returns the address of an variable. the variable. * Pointer to a variable. *a; will pointer to a variable. If Condition is true ? Then ?: Conditional Expression value X : Otherwise value Y Operators Precedence in C Operator precedence determines the grouping of terms in an expression. This affects how an expression is evaluated. Certain operators have higher precedence than others; for example, the multiplication operator has higher precedence than the addition operator. For example, x = 7 + 3 * 2; here, x is assigned 13, not 20 because operator * has higher precedence than +, so it first gets multiplied with 3*2 and then adds into 7. Here, operators with the highest precedence appear at the top of the table, those with the lowest appear at the bottom. Within an expression, higher precedence operators will be evaluated first. Category Operator Associativity Postfix () [] ->. ++ - - Left to right Unary + - ! ~ ++ - - (type)* & sizeof Right to left Multiplicative */% Left to right Additive +- Left to right Shift > Left to right Relational < >= Left to right Equality == != Left to right Bitwise AND & Left to right Bitwise XOR ^ Left to right Bitwise OR | Left to right TUTORIALS POINT Simply Easy Learning Page 33 Logical AND && Left to right Logical OR || Left to right Conditional ?: Right to left Assignment = += -= *= /= %=>>= 0; i--) { printf("Address of var[%d] = %x\n", i, ptr ); printf("Value of var[%d] = %d\n", i, *ptr ); ptr--; } return 0; } When the above code is compiled and executed, it produces result something as follows: Address of var = bfedbcd8 Value of var = 200 Address of var = bfedbcd4 Value of var = 100 Address of var = bfedbcd0 Value of var = 10 Pointer Comparisons Pointers may be compared by using relational operators, such as ==,. If p1 and p2 point to variables that are related to each other, such as elements of the same array, then p1 and p2 can be meaningfully compared. The following program modifies the previous example one by incrementing the variable pointer so long as the address to which it points is either less than or equal to the address of the last element of the array, which is &var[MAX - 1]: #include TUTORIALS POINT Simply Easy Learning Page 83 const int MAX = 3; int main () { int var[] = {10, 100, 200}; int i, *ptr; ptr = var; i = 0; while ( ptr operator as follows: struct_pointer->title; Let us re-write above example using structure pointer, hope this will be easy for you to understand the concept: #include TUTORIALS POINT Simply Easy Learning Page 97 #include struct Books { char title; char author; char subject; int book_id; }; void printBook( struct Books *book ); int main( ) { struct Books Book1; struct Books Book2; strcpy( Book1.title, "C Programming"); strcpy( Book1.author, "Nuha Ali"); strcpy( Book1.subject, "C Programming Tutorial"); Book1.book_id = 6495407; strcpy( Book2.title, "Telecom Billing"); strcpy( Book2.author, "Zara Ali"); strcpy( Book2.subject, "Telecom Billing Tutorial"); Book2.book_id = 6495700; printBook( &Book1 ); printBook( &Book2 ); return 0; } void printBook( struct Books *book ) { printf( "Book title : %s\n", book->title); printf( "Book author : %s\n", book->author); printf( "Book subject : %s\n", book->subject); printf( "Book book_id : %d\n", book->book_id); } When the above code is compiled and executed, it produces the following result: Book title : C Programming Book author : Nuha Ali Book subject : C Programming Tutorial Book book_id : 6495407 Book title : Telecom Billing Book author : Zara Ali TUTORIALS POINT Simply Easy Learning Page 98 Book subject : Telecom Billing Tutorial Book book_id : 6495700 TUTORIALS POINT Simply Easy Learning Page 99 CHAPTER 18 C Unions A union is a special data type available in C that enables you to store different data types in the same memory location. You can define a union with many members, but only one member can contain a value at any given time. Unions provide an efficient way of using the same memory location for multi-purpose. Defining a Union To define a union, you must use the union statement in very similar was as you did while defining structure. The union statement defines a new data type, with more than one member for your program. The format of the union statement is as follows: union [union tag] { member definition; member definition;... member definition; } [one or more union variables]; The union tag is optional and each member definition is a normal variable definition, such as int i; or float f; or any other valid variable definition. At the end of the union's definition, before the final semicolon, you can specify one or more union variables but it is optional. Here is the way you would define a union type named Data which has the three members i, f, and str: union Data { int i; float f; char str; } data; Now, a variable of Data type can store an integer, a floating-point number, or a string of characters. This means that a single variable i.e. same memory location can be used to store multiple types of data. You can use any built-in or user defined data types inside a union based on your requirement. TUTORIALS POINT Simply Easy Learning Page 100 The memory occupied by a union will be large enough to hold the largest member of the union. For example, in above example Data type will occupy 20 bytes of memory space because this is the maximum space which can be occupied by character string. Following is the example which will display total memory size occupied by the above union: #include #include union Data { int i; float f; char str; }; int main( ) { union Data data; printf( "Memory size occupied by data : %d\n", sizeof(data)); return 0; } When the above code is compiled and executed, it produces the following result: Memory size occupied by data : 20 Accessing Union Members To access any member of a union, we use the member access operator (.). The member access operator is coded as a period between the union variable name and the union member that we wish to access. You would use union keyword to define variables of union type. Following is the example to explain usage of union: #include #include union Data { int i; float f; char str; }; int main( ) { union Data data; data.i = 10; data.f = 220.5; strcpy( data.str, "C Programming"); printf( "data.i : %d\n", data.i); printf( "data.f : %f\n", data.f); TUTORIALS POINT Simply Easy Learning Page 101 printf( "data.str : %s\n", data.str); return 0; } When the above code is compiled and executed, it produces the following result: data.i : 1917853763 data.f : 4122360580327794860452759994368.000000 data.str : C Programming Here, we can see that values of i and f members of union got corrupted because final value assigned to the variable has occupied the memory location and this is the reason that the value if str member is getting printed very well. Now let's look into the same example once again where we will use one variable at a time which is the main purpose of having union: #include #include union Data { int i; float f; char str; }; int main( ) { union Data data; data.i = 10; printf( "data.i : %d\n", data.i); data.f = 220.5; printf( "data.f : %f\n", data.f); strcpy( data.str, "C Programming"); printf( "data.str : %s\n", data.str); return 0; } When the above code is compiled and executed, it produces the following result: data.i : 10 data.f : 220.500000 data.str : C Programming Here, all the members are getting printed very well because one member is being used at a time. TUTORIALS POINT Simply Easy Learning Page 102 CHAPTER 19 Bit Fields S uppose your C program contains a number of TRUE/FALSE variables grouped in a structure called status, as follows: struct { unsigned int widthValidated; unsigned int heightValidated; } status; This structure requires 8 bytes of memory space but in actual we are going to store either 0 or 1 in each of the variables. The C programming language offers a better way to utilize the memory space in such situation. If you are using such variables inside a structure then you can define the width of a variable which tells the C compiler that you are going to use only those number of bytes. For example, above structure can be re-written as follows: struct { unsigned int widthValidated : 1; unsigned int heightValidated : 1; } status; Now, the above structure will require 4 bytes of memory space for status variable but only 2 bits will be used to store the values. If you will use up to 32 variables each one with a width of 1 bit , then also status structure will use 4 bytes, but as soon as you will have 33 variables, then it will allocate next slot of the memory and it will start using 64 bytes. Let us check the following example to understand the concept: #include #include struct { unsigned int widthValidated; unsigned int heightValidated; } status1; TUTORIALS POINT Simply Easy Learning Page 103 struct { unsigned int widthValidated : 1; unsigned int heightValidated : 1; } status2; int main( ) { printf( "Memory size occupied by status1 : %d\n", sizeof(status1)); printf( "Memory size occupied by status2 : %d\n", sizeof(status2)); return 0; } When the above code is compiled and executed, it produces the following result: Memory size occupied by status1 : 8 Memory size occupied by status2 : 4 Bit Field Declaration The declaration of a bit-field has the form inside a structure: struct { type [member_name] : width ; }; Below the description of variable elements of a bit field: Elements Description An integer type that determines how the bit-field's value is interpreted. The type may type be int, signed int, unsigned int. member_name The name of the bit-field. The number of bits in the bit-field. The width must be less than or equal to the bit width width of the specified type. The variables defined with a predefined width are called bit fields. A bit field can hold more than a single bit for example if you need a variable to store a value from 0 to 7 only then you can define a bit field with a width of 3 bits as follows: struct { unsigned int age : 3; } Age; The above structure definition instructs C compiler that age variable is going to use only 3 bits to store the value, if you will try to use more than 3 bits then it will not allow you to do so. Let us try the following example: TUTORIALS POINT Simply Easy Learning Page 104 #include #include struct { unsigned int age : 3; } Age; int main( ) { Age.age = 4; printf( "Sizeof( Age ) : %d\n", sizeof(Age) ); printf( "Age.age : %d\n", Age.age ); Age.age = 7; printf( "Age.age : %d\n", Age.age ); Age.age = 8; printf( "Age.age : %d\n", Age.age ); return 0; } When the above code is compiled it will compile with warning and when executed, it produces the following result: Sizeof( Age ) : 4 Age.age : 4 Age.age : 7 Age.age : 0 TUTORIALS POINT Simply Easy Learning Page 105 CHAPTER 20 Typedef T he C programming language provides a keyword called typedef, which you can use to give a type a new name. Following is an example to define a term BYTE for one-byte numbers: typedef unsigned char BYTE; After this type definitions, the identifier BYTE can be used as an abbreviation for the type unsigned char, for example: BYTE b1, b2; By convention, uppercase letters are used for these definitions to remind the user that the type name is really a symbolic abbreviation, but you can use lowercase, as follows: typedef unsigned char byte; You can use typedef to give a name to user defined data type as well. For example you can use typedef with structure to define a new data type and then use that data type to define structure variables directly as follows: #include #include typedef struct Books { char title; char author; char subject; int book_id; } Book; int main( ) { Book book; strcpy( book.title, "C Programming"); strcpy( book.author, "Nuha Ali"); strcpy( book.subject, "C Programming Tutorial"); TUTORIALS POINT Simply Easy Learning Page 106 book.book_id = 6495407; printf( "Book title : %s\n", book.title); printf( "Book author : %s\n", book.author); printf( "Book subject : %s\n", book.subject); printf( "Book book_id : %d\n", book.book_id); return 0; } When the above code is compiled and executed, it produces the following result: Book title : C Programming Book author : Nuha Ali Book subject : C Programming Tutorial Book book_id : 6495407 typedef vs #define The #define is a C-directive which is also used to define the aliases for various data types similar to typedef but with three differences:  The typedef is limited to giving symbolic names to types only where as #define can be used to define alias for values as well, like you can define 1 as ONE etc.  The typedef interpretation is performed by the compiler where as #define statements are processed by the pre-processor. Following is a simplest usage of #define: #include #define TRUE 1 #define FALSE 0 int main( ) { printf( "Value of TRUE : %d\n", TRUE); printf( "Value of FALSE : %d\n", FALSE); return 0; } When the above code is compiled and executed, it produces the following result: Value of TRUE : 1 Value of FALSE : 0 TUTORIALS POINT Simply Easy Learning Page 107 CHAPTER 21 Input & Output W hen we are saying Input that means to feed some data into program. This can be given in the form of file or from command line. C programming language provides a set of built-in functions to read given input and feed it to the program as per requirement. When we are saying Output that means to display some data on screen, printer or in any file. C programming language provides a set of built-in functions to output the data on the computer screen as well as you can save that data in text or binary files. The Standard Files C programming language treats all the devices as files. So devices such as the display are addressed in the same way as files and following three file are automatically opened when a program executes to provide access to the keyboard and screen. Standard File File Pointer Device Standard input stdin Keyboard Standard output stdout Screen Standard error stderr Your screen The file points are the means to access the file for reading and writing purpose. This section will explain you how to read values from the screen and how to print the result on the screen. The getchar() & putchar() functions The int getchar(void) function reads the next available character from the screen and returns it as an integer. This function reads only single character at a time. You can use this method in the loop in case you want to read more than one characters from the screen. The int putchar(int c) function puts the passed character on the screen and returns the same character. This function puts only single character at a time. You can use this method TUTORIALS POINT Simply Easy Learning Page 108 in the loop in case you want to display more than one character on the screen. Check the following example: #include int main( ) { int c; printf( "Enter a value :"); c = getchar( ); printf( "\nYou entered: "); putchar( c ); return 0; } When the above code is compiled and executed, it waits for you to input some text when you enter a text and press enter then program proceeds and reads only a single character and displays it as follows: $./a.out Enter a value : this is test You entered: t The gets() & puts() functions The char *gets(char *s) function reads a line from stdin into the buffer pointed to by s until either a terminating newline or EOF. The int puts(const char *s) function writes the string s and a trailing newline to stdout. #include int main( ) { char str; printf( "Enter a value :"); str = gets( str ); printf( "\nYou entered: "); puts( str ); return 0; } When the above code is compiled and executed, it waits for you to input some text when you enter a text and press enter then program proceeds and reads the complete line till end and displays it as follows: $./a.out Enter a value : this is test TUTORIALS POINT Simply Easy Learning Page 109 You entered: This is test The scanf() and printf() functions The int scanf(const char *format,...) function reads input from the standard input stream stdin and scans that input according to format provided. The int printf(const char *format,...) function writes output to the standard output stream stdout and produces output according to a format provided. The format can be a simple constant string, but you can specify %s, %d, %c, %f, etc., to print or read strings, integer, character or float respectively. There are many other formatting options available which can be used based on requirements. For a complete detail you can refer to a man page for these function. For now let us proceed with a simple example which makes things clear: #include int main( ) { char str; int i; printf( "Enter a value :"); scanf("%s %d", str, &i); printf( "\nYou entered: %s, %d ", str, i); return 0; } When the above code is compiled and executed, it waits for you to input some text when you enter a text and press enter then program proceeds and reads the input and displays it as follows: $./a.out Enter a value : seven 7 You entered: seven 7 Here, it should be noted that scanf() expect input in the same format as you provided %s and %d, which means you have to provide valid input like "string integer", if you provide "string string" or "integer integer" then it will be assumed as wrong input. Second, while reading a string scanf() stops reading as soon as it encounters a space so "this is test" are three strings for scanf(). TUTORIALS POINT Simply Easy Learning Page 110 CHAPTER 22 File I/O L ast chapter explained about standard input and output devices handled by C programming language. This chapter we will see how C programmers can create, open, close text or binary files for their data storage. A file represents a sequence of bytes, does not matter if it is a text file or binary file. C programming language provides access on high level functions as well as low level (OS level) calls to handle file on your storage devices. This chapter will take you through important calls for the file management. Opening Files You can use the fopen( ) function to create a new file or to open an existing file, this call will initialize an object of the type FILE, which contains all the information necessary to control the stream. Following is the prototype of this function call: FILE *fopen( const char * filename, const char * mode ); Here, filename is string literal, which you will use to name your file and access mode can have one of the following values: Mode Description r Opens an existing text file for reading purpose. Opens a text file for writing, if it does not exist then a new file is created. Here your program will w start writing content from the beginning of the file. Opens a text file for writing in appending mode, if it does not exist then a new file is created. a Here your program will start appending content in the existing file content. r+ Opens a text file for reading and writing both. Opens a text file for reading and writing both. It first truncate the file to zero length if it exists w+ otherwise create the file if it does not exist. Opens a text file for reading and writing both. It creates the file if it does not exist. The reading a+ will start from the beginning but writing can only be appended. TUTORIALS POINT Simply Easy Learning Page 111 If you are going to handle binary files then you will use below mentioned access modes instead of the above mentioned: "rb", "wb", "ab", "ab+", "a+b", "wb+", "w+b", "ab+", "a+b" Closing a File To close a file, use the fclose( ) function. The prototype of this function is: int fclose( FILE *fp ); The fclose( ) function returns zero on success, or EOF if there is an error in closing the file. This function actually, flushes any data still pending in the buffer to the file, closes the file, and releases any memory used for the file. The EOF is a constant defined in the header file stdio.h. There are various functions provide by C standard library to read and write a file character by character or in the form of a fixed length string. Let us see few of the in the next section. Writing a File Following is the simplest function to write individual characters to a stream: int fputc( int c, FILE *fp ); The function fputc() writes the character value of the argument c to the output stream referenced by fp. It returns the written character written on success otherwise EOF if there is an error. You can use the following functions to write a null-terminated string to a stream: int fputs( const char *s, FILE *fp ); The function fputs() writes the string s to the output stream referenced by fp. It returns a non-negative value on success, otherwise EOF is returned in case of any error. You can use int fprintf(FILE *fp,const char *format,...) function as well to write a string into a file. Try the following example: #include main() { FILE *fp; fp = fopen("/tmp/test.txt", "w+"); fprintf(fp, "This is testing for fprintf...\n"); fputs("This is testing for fputs...\n", fp); fclose(fp); } TUTORIALS POINT Simply Easy Learning Page 112 When the above code is compiled and executed, it creates a new file test.txt in /tmp directory and writes two lines using two different functions. Let us read this file in next section. Reading a File Following is the simplest function to read a single character from a file: int fgetc( FILE * fp ); The fgetc() function reads a character from the input file referenced by fp. The return value is the character read, or in case of any error it returns EOF. The following functions allow you to read a string from a stream: char *fgets( char *buf, int n, FILE *fp ); The functions fgets() reads up to n - 1 characters from the input stream referenced by fp. It copies the read string into the buffer buf, appending a null character to terminate the string. If this function encounters a newline character '\n' or the end of the file EOF before they have read the maximum number of characters, then it returns only the characters read up to that point including new line character. You can also use int fscanf(FILE *fp, const char *format,...) function to read strings from a file but it stops reading after the first space character encounters. #include main() { FILE *fp; char buff; fp = fopen("/tmp/test.txt", "r"); fscanf(fp, "%s", buff); printf("1 : %s\n", buff ); fgets(buff, 255, (FILE*)fp); printf("2: %s\n", buff ); fgets(buff, 255, (FILE*)fp); printf("3: %s\n", buff ); fclose(fp); } When the above code is compiled and executed, it reads the file created in previous section and produces the following result: 1 : This 2: is testing for fprintf... TUTORIALS POINT Simply Easy Learning Page 113 3: This is testing for fputs... Let's see a little more detail about what happened here. First fscanf() method read just This because after that it encountered a space, second call is for fgets() which read the remaining line till it encountered end of line. Finally last call fgets() read second line completely. Binary I/O Functions There are following two functions, which can be used for binary input and output: size_t fread(void *ptr, size_t size_of_elements, size_t number_of_elements, FILE *a_file); size_t fwrite(const void *ptr, size_t size_of_elements, size_t number_of_elements, FILE *a_file); Both of these functions should be used to read or write blocks of memories - usually arrays or structures. TUTORIALS POINT Simply Easy Learning Page 114 CHAPTER 23 Preprocessors T he C Preprocessor is not part of the compiler, but is a separate step in the compilation process. In simplistic terms, a C Preprocessor is just a text substitution tool and they instruct compiler to do required pre-processing before actual compilation. We'll refer to the C Preprocessor as the CPP. All preprocessor commands begin with a pound symbol (#). It must be the first nonblank character, and for readability, a preprocessor directive should begin in first column. Following section lists down all important preprocessor directives: Directive Description #define Substitutes a preprocessor macro #include Inserts a particular header from another file #undef Undefines a preprocessor macro #ifdef Returns true if this macro is defined #ifndef Returns true if this macro is not defined #if Tests if a compile time condition is true #else The alternative for #if #elif #else an #if in one statement #endif Ends preprocessor conditional #error Prints error message on stderr #pragma Issues special commands to the compiler, using a standardized method Preprocessors Examples Analyze following examples to understand various directives. #define MAX_ARRAY_LENGTH 20 TUTORIALS POINT Simply Easy Learning Page 115 This directive tells the CPP to replace instances of MAX_ARRAY_LENGTH with 20. Use #define for constants to increase readability. #include #include "myheader.h" These directives tell the CPP to get stdio.h from System Libraries and add the text to the current source file. The next line tells CPP to get myheader.h from the local directory and add the content to the current source file. #undef FILE_SIZE #define FILE_SIZE 42 This tells the CPP to undefine existing FILE_SIZE and define it as 42. #ifndef MESSAGE #define MESSAGE "You wish!" #endif This tells the CPP to define MESSAGE only if MESSAGE isn't already defined. #ifdef DEBUG #endif This tells the CPP to do the process the statements enclosed if DEBUG is defined. This is useful if you pass the -DDEBUG flag to gcc compiler at the time of compilation. This will define DEBUG, so you can turn debugging on and off on the fly during compilation. Predefined Macros ANSI C defines a number of macros. Although each one is available for your use in programming, the predefined macros should not be directly modified. Macro Description __DATE__ The current date as a character literal in "MMM DD YYYY" format __TIME__ The current time as a character literal in "HH:MM:SS" format __FILE__ This contains the current filename as a string literal. __LINE__ This contains the current line number as a decimal constant. __STDC__ Defined as 1 when the compiler complies with the ANSI standard. Let's try the following example: #include main() TUTORIALS POINT Simply Easy Learning Page 116 { printf("File :%s\n", __FILE__ ); printf("Date :%s\n", __DATE__ ); printf("Time :%s\n", __TIME__ ); printf("Line :%d\n", __LINE__ ); printf("ANSI :%d\n", __STDC__ ); } When the above code in a file test.c is compiled and executed, it produces the following result: File :test.c Date :Jun 2 2012 Time :03:36:24 Line :8 ANSI :1 Preprocessor Operators The C preprocessor offers following operators to help you in creating macros: Macro Continuation (\) A macro usually must be contained on a single line. The macro continuation operator is used to continue a macro that is too long for a single line. For example: #define message_for(a, b) \ printf(#a " and " #b ": We love you!\n") Stringize (#) The stringize or number-sign operator ('#'), when used within a macro definition, converts a macro parameter into a string constant. This operator may be used only in a macro that has a specified argument or parameter list. For example: #include #define message_for(a, b) \ printf(#a " and " #b ": We love you!\n") int main(void) { message_for(Carole, Debra); return 0; } When the above code is compiled and executed, it produces the following result: TUTORIALS POINT Simply Easy Learning Page 117 Carole and Debra: We love you! Token Pasting (##) The token-pasting operator (##) within a macro definition combines two arguments. It permits two separate tokens in the macro definition to be joined into a single token. For example: #include #define tokenpaster(n) printf ("token" #n " = %d", token##n) int main(void) { int token34 = 40; tokenpaster(34); return 0; } When the above code is compiled and executed, it produces the following result: token34 = 40 How it happened, because this example results in the following actual output from the preprocessor: printf ("token34 = %d", token34); This example shows the concatenation of token##n into token34 and here we have used both stringize and token-pasting. The defined() Operator The preprocessor defined operator is used in constant expressions to determine if an identifier is defined using #define. If the specified identifier is defined, the value is true (non-zero). If the symbol is not defined, the value is false (zero). The defined operator is specified as follows: #include #if !defined (MESSAGE) #define MESSAGE "You wish!" #endif int main(void) { printf("Here is the message: %s\n", MESSAGE); return 0; } TUTORIALS POINT Simply Easy Learning Page 118 When the above code is compiled and executed, it produces the following result: Here is the message: You wish! Parameterized Macros One of the powerful functions of the CPP is the ability to simulate functions using parameterized macros. For example, we might have some code to square a number as follows: int square(int x) { return x * x; } We can rewrite above code using a macro as follows: #define square(x) ((x) * (x)) Macros with arguments must be defined using the #define directive before they can be used. The argument list is enclosed in parentheses and must immediately follow the macro name. Spaces are not allowed between and macro name and open parenthesis. For example: #include #define MAX(x,y) ((x) > (y) ? (x) : (y)) int main(void) { printf("Max between 20

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