LectENG1008_T1_IntroductionToComputerAndCprogramming.pdf

Programming Topic 1  Introduction to Programming Languages  Introduction to C Programming T1-1 Introduction to Programming Languages T1-2  Programming Languages  Programmers write instructions in various program...

Programming Topic 1  Introduction to Programming Languages  Introduction to C Programming T1-1 Introduction to Programming Languages T1-2  Programming Languages  Programmers write instructions in various programming languages, some directly understandable by computers and others requiring intermediate translation steps.  Any computer can directly understand only its own machine language, defined by its hardware design.  Machine languages generally consist of numbers (ultimately reduced to 1s and 0s). Such languages are cumbersome for humans.  Programming in machine language—the numbers that computers could directly understand—was simply too slow and tedious for most programmers.  Instead, they began using English like abbreviations to represent elementary operations.  These abbreviations formed the basis of assembly languages.  Translator programs called assemblers were developed to convert assembly-language programs to machine language. T1-3  Programming Languages  Although assembly-language code is clearer to humans, it’s incomprehensible to computers until translated to machine language.  To speed the programming process even further, high-level languages were developed in which single statements could be written to accomplish substantial tasks.  High-level languages allow you to write instructions that look almost like everyday English and contain commonly used mathematical expressions.  Translator programs called compilers convert high-level language programs into machine language.  Interpreter programs were developed to execute high-level language programs directly, although more slowly than compiled programs.  Scripting languages such as JavaScript and PHP are processed by interpreters. T1-4 Source : “C How to Program”, Pearson Education Inc  The C Programming language  C evolved from two previous languages, BCPL and B.  BCPL was developed in 1967 by Martin Richards as a language for writing operating-systems software and compilers.  Ken Thompson modeled many features in his B language after their counterparts in BCPL, and in 1970 he used B to create early versions of the UNIX operating system at Bell Laboratories.  The C language was evolved from B by Dennis Ritchie at Bell Laboratories and was originally implemented in 1972.  C initially became widely known as the development language of the UNIX operating system.  Many of todays leading operating systems are written in C &/or C++  C is mostly hardware independent.  With careful design, it’s possible to write C programs that are portable to most computers. T1-5  The C Programming language Built for Performance  C is widely used to develop systems that demand performance, such as operating systems, embedded systems, real-time systems and communications systems (Figure 1.5). T1-6 Source : “C How to Program”, Pearson Education Inc  The C Programming language  By the late 1970s, C had evolved into what is now referred to as “traditional C.” The publication in 1978 of Kernighan and Ritchie’s book, The C Programming Language, drew wide attention to the language.  Standardization The rapid expansion of C over various types of computers (sometimes called hardware platforms) led to many variations that were similar but often incompatible. In 1989, the C standard was approved; this standard was updated in 1999 and is often referred to as C99.  The New C Standard - The new C standard (referred to as C11) approved in 2011 and updated in 2018 (C18) refines and expands the capabilities of C. - Next update is likely to be released in 2022. “Programming Language C -C2x Charter.” Accessed 28 August 2020. https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2086.htm T1-7 Source : “C How to Program”, Pearson Education Inc  C Standard Library  Avoid reinventing the wheel.  Instead, use existing pieces—this is called software reuse.  When programming in C you’ll typically use the following building blocks: C Standard Library functions Open-source C library functions Functions you create yourself Functions other people (whom you trust) have created and made available to you T1-8  C Standard Library  The advantage of creating your own functions is that you’ll know exactly how they work. You’ll be able to examine the C code.  The disadvantage is the time-consuming effort that goes into designing, developing and debugging T1-9 Source : “C How to Program”, Pearson Education Inc  Other languages: C++  C++ was developed by Bjarne Stroustrup at Bell Laboratories.  It has its roots in C, providing a number of features that “spruce up” the C language.  More important, it provides capabilities for object-oriented programming.  Objects are essentially reusable software components that model items in the real world.  Using a modular, object-oriented design and implementation approach can make software development groups more productive. T1-10  Other languages: Python  Python is an object-oriented language, developed by Guido van Rossum and was released in 1991.  Rapidly became popular for educational and scientific computing due to the following reasons: - Open-source, free and widely available - Supported by a massive open-source community - Relatively easy to learn - Code is easier to read than many other popular programming languages - Developer productivity is enhanced with extensive standard libraries and thousands of third-party open-source libraries - Popular in web development, AI and data science, which are currently hot areas of growth, and also financial community. T1-11  C Programming Development  C systems generally consist of several parts: a program development environment, the language and the C Standard Library.  C programs typically go through six phases to be executed (Fig. 1.7).  These are: edit, preprocess, compile, link, load and execute.  Although C How to Program, 9/e is a generic C textbook (written independently of the details of any particular operating system), we concentrate in this section on a typical Linux-based C system. T1-12  Phase 1 Creating the program  Phase 1 consists of editing a file.  This is accomplished with an editor program.  Two editors widely used on Linux systems are vi and emacs.  Software packages for the C/C++ integrated program development environments such as Eclipse, Microsoft Visual Studio and Code:Blocks have editors that are integrated into the programming environment.  You type a C program with the editor, make corrections if necessary, then store the program on a secondary storage device such as a hard disk.  C program file names should end with the.c extension T1-13  Phases 2 and 3: Preprocessing and Compiling  In Phase 2, you give the command to compile the program.  The compiler translates the C program into machine language-code (also referred to as object code).  In a C system, a preprocessor program executes automatically before the compiler’s translation phase begins.  The C preprocessor obeys special commands called preprocessor directives, which indicate that certain manipulations are to be performed on the program before compilation.  These manipulations usually consist of including other files in the file to be compiled and performing various text replacements. T1-14  Phases 2 and 3: Preprocessing and Compiling  In Phase 3, the compiler translates the C program into machine-language code.  A syntax error occurs when the compiler cannot recognize a statement because it violates the rules of the language.  Syntax errors are also called compile errors, or compile-time errors. T1-15  Phase 4 Linking  The next phase is called linking.  C programs typically contain references to functions defined elsewhere, such as in the standard libraries or in the private libraries of groups of programmers working on a particular project.  The object code produced by the C compiler typically contains “holes” due to these missing parts.  A linker links the object code with the code for the missing functions to produce an executable image (with no missing pieces).  On a typical Linux system, the command to compile and link a program is called gcc (the GNU compiler). T1-16  Phase 4 Linking  To compile and link a program named welcome.c type  gcc welcome.c  at the Linux prompt and press the Enter key (or Return key).  Note: Linux commands are case sensitive; make sure that each c is lowercase and that the letters in the filename are in the appropriate case.  If the program compiles and links correctly, a file called a.out is produced. In Windows, a.exe is produced  This is the executable image of our welcome.c program.  To specify the output filename, use the ‘-o’ flag and type  gcc welcome.c –o welcome  this will produce a welcome.out file in Linux or welcome.exe file in Windows T1-17  Phase 5 Loading  The next phase is called loading.  Before a program can be executed, the program must first be placed in memory.  This is done by the loader, which takes the executable image from disk and transfers it to memory.  Additional components from shared libraries that support the program are also loaded. T1-18  Phase 6 Executing  Finally, the computer, under the control of its CPU, executes the program one instruction at a time.  To load and execute the program on a Linux system, type./a.out at the Linux prompt and press Enter. On a Windows system, type a and press Enter. T1-19  Phases 1 to 4 T1-20 Source : “C How to Program”, Pearson Education Inc  Phases 5 & 6 T1-21 Source : “C How to Program”, Pearson Education Inc  Problems during execution  Programs do not always work on the first try.  Each of the preceding phases can fail because of various errors that we’ll discuss.  For example, an executing program might attempt to divide by zero (an illegal operation on computers just as in arithmetic).  This would cause the computer to display an error message.  You would then return to the edit phase, make the necessary corrections and proceed through the remaining phases again to determine that the corrections work properly. T1-22 Source : “C How to Program”, Pearson Education Inc  Standard Input, Output and Error  Most C programs input and/or output data.  Certain C functions take their input from stdin (the standard input stream), which is normally the keyboard, but stdin can be connected to another stream.  Data is often output to stdout (the standard output stream), which is normally the computer screen, but stdout can be connected to another stream.  When we say that a program prints a result, we normally mean that the result is displayed on a screen.  Data may be output to devices such as disks and printers. T1-23  Standard Input, Output and Error  There is also a standard error stream referred to as stderr.  The stderr stream (normally connected to the screen) is used for displaying error messages.  It’s common to route regular output data, i.e., stdout, to a device other than the screen while keeping stderr assigned to the screen so that the user can be immediately informed of errors. T1-24 Introduction to C Programming T1-25  Objectives  To write a simple C program  To use basic data types and variables  To learn about memory concepts  To perform basic Input from keyboard / Output to screen  To perform C Arithmetic operations  C’s keywords T1-26  A simple C program  Simple C program to print a line of text T1-27 Source : “C How to Program”, Pearson Education Inc  A simple C program  Comments  Insert comments for documentation improves readability helps other people to read and understand your code  Begins with // or to use  Ignored by the C compiler machine object code is not generated for it will not perform any action when the program is run  #include  a directive to the C pre-processor  processed by the C pre-processor before compilation  to include the contents of the standard input/output header; shows standard I/O operations T1-28  A simple C program  Blank lines and White spaces  blank lines, space (characters), tab (characters)/indent improves readability  these are known as white space  normally ignored by the compiler  main function – int main(void)  (main) part of every C program; one of the functions  every C program begins execution at the function main  keyword int to the left of main indicates that the main function will return an integer value  the void in parentheses indicates that main does not receive any data T1-29  A simple C program {}  left brace { begins the body of every function  the corresponding right brace } ends each function  code between the pair of braces is a block  Output statement  printf(“Welcome to C!\n”);  causes the computer to perform the print/output action  The string “Welcome to C!” is printed followed by the newline \n  The blackslash \ is called an escape character T1-30  Escape sequence T1-31 Source : “C How to Program”, Pearson Education Inc  Linker and Executables  Linker  standard library functions (e.g. printf, scantf) are not part of the C programming language  the C compiler does not know where the standard library functions are  the linker locates the library functions and inserts the correct calls to the library functions in the object code  Executables  the object program is complete and can be executed  To load and execute the executables ./a or./programname T1-32  Basic Data Types  Basic data types  int (integer, a whole number) Size 4 bytes  float (floating point, real numbers, has decimal point) Size 4 bytes  double (double precision floating point number) Size 8 bytes  char (character) Size 1 byte Check out code at  sizeof operator http://tpcg.io/_WHDQ7Z  unsigned and signed  void T1-33  Variables and Memory concepts  Variables  Variables are created with names that are associated with memory locations in the computer system  Each variable is defined with a name and data type, and has a value and location in the computer’s memory  When a new value is placed into a variable, it will replace the previous value  Reading variables in memory is non-destructive – it will not change the value stored in it  Variable name – valid Identifiers and case sensitivity  an identifier consists of a series of characters (letter, digits and underscores; does not begin with a digit)  C is case sensitive T1-34  Basic I/O  Output to screen  standard library function printf  e.g. printf(“Hello World\n”);  e.g. int a = 1; printf(“Today is Day %d\n”, a);  Input from keyboard  Standard library function scanf  e.g. int b; scanf(“%d”,&b); first part - %d : is the format control string second part - &b : provides to scanf the address in memory of the variable b T1-35  Arithmetic in C  C Arithmetic operators (ref Figure 2.9)  Addition +, Subtraction -, Multiplication *  Division / and Reminder or mod %  What is 7/4 ? What is 7%4  Division by 0 error T1-36 Source : “C How to Program”, Pearson Education Inc  Arithmetic in C  Parentheses for grouping subexpressions  e.g. (a * b) / (c + d)  Rules of Operator Precedence  similar rules to algebra  parentheses has the highest level of precedence T1-37 Source : “C How to Program”, Pearson Education Inc  Arithmetic in C T1-38 Source : “C How to Program”, Pearson Education Inc  Addition C program T1-39 Source : “C How to Program”, Pearson Education Inc  Equality and Relational Operators T1-40 Source : “C How to Program”, Pearson Education Inc  C keywords Do not use these keywords as identifiers as they have special meaning to the compiler T1-41 Source : “C How to Program”, Pearson Education Inc