Introduction to C Programming

Basics of C Programming

• C is a general-purpose, procedural, imperative programming language
• It was developed by Dennis M. Ritchie in 1972 at Bell Telephone Laboratories
• C was created to develop the UNIX operating system
• It is among the most widely used languages, often fluctuating in popularity with Java

Why Learn C?

• C is essential for students and professionals in software development
• It is easy to learn
• C is a structured language
• It produces efficient programs
• It is capable of handling low-level activities
• It can be compiled across various computer platforms

Facts About C

• C was used to write UNIX
• It is a successor to the B language, introduced in the early 1970s
• The language was formalized in 1988 by ANSI
• The UNIX OS was entirely written in C
• Today, C is a popular System Programming Language
• Most state-of-the-art software has been implemented using C
• Popular systems like Linux OS and RDBMS MySQL are written in C

Printing "Hello World" in C

• Below is the basic code

#include <stdio.h>

int main() {
    printf("Hello, World! \n");
    return 0;
}

Applications of C

• C was initially for system development, particularly for operating system programs
• C produces code that runs nearly as fast as assembly language
• C is used in:
• Operating Systems
• Language Compilers
• Assemblers
• Text Editors
• Print Spoolers
• Network Drivers
• Modern Programs
• Databases
• Language Interpreters
• Utilities

Hello World Example: Program Components

• Preprocessor Commands
• Functions
• Variables
• Statements & Expressions
• Comments

Code to Print "Hello World"

#include <stdio.h>

int main() {
    printf("Hello, World! \n");
    return 0;
}

Parts of the "Hello World" Program

• #include <stdio.h> is a preprocessor command that includes the "stdio.h" file before compilation
• int main() is the main function where execution starts
• /*...*/is ignored by the compiler, used for comments.
• printf(...) is a C function that displays "Hello, World!" on the screen
• return 0; terminates the main function and returns the value 0

Compiling and Executing a C Program

• Open a text editor and write the code
• Save the file as hello.c
• Open a command prompt in the directory where the file is saved
• Compile the code using gcc hello.c
• If there are no errors, an executable file a.out will be generated
• Run the program by typing ./a.out
• The output "Hello, World!" will be shown on the screen

Tokens in C

• A C program consists of tokens
• A token can be a keyword, identifier, constant, string literal, or symbol
• For example, the statement printf("Hello, World! \n"); has five tokens in it

Semicolons

• the semicolon is a statement terminator
• Each statement must end with a semicolon to indicate the end of a logical entity
• printf("Hello, World! \n"); & return 0; are two statements

Comments

• Comments are ignored by the compiler and serve as helping text
• They start with /* and end with */
• They cannot be nested or occur within string or character literals

Identifiers

• A C identifier names a variable, function, or user-defined item
• They start with a letter (A-Z, a-z) or underscore _, followed by letters, underscores, and digits (0-9)
• Punctuation characters are not allowed
• C is case-sensitive, so Manpower and manpower are different identifiers

Keywords

• C has reserved words that cannot be used as constants, variables, or identifiers

Whitespace

• A blank line (containing only whitespace or a comment) is ignored by the C compiler
• Whitespace includes blanks, tabs, newline characters, and comments
• Whitespace separates parts of a statement, such as int age;

Header Files in C

• Header files have a .h extension
• They contain C function declarations and macro definitions to be shared across source files
• There are programmer-written files and compiler-provided files
• #include preprocessing directive is used to include header files
• Including a header file is like copying its content, but is done to prevent errors
• Constants, macros, global variables, and function prototypes are in header files

Include Syntax

• User and system header files are included using the #include directive
• System header files #include are searched for in standard system directories, prepend with -I to specify a different location
• User header files #include "file" are searched for in the current directory

Include Operation

• The #include directive tells the C preprocessor to scan the specified file before continuing
• The output from the preprocessor contains the generated output, followed by the included file's output

Data Types

• Data types in C declare variables or functions of different types
• The type of variable determines memory space and interpretation

Basic Data Types

• Basic Types: Arithmetic types
• Integer types
• Floating-point types.
• Enumerated types: Arithmetic types
• Used to define variables that only assign discrete integer values
• The type void: Indicates no value is available
• Derived types:
• Pointer types
• Array types
• Structure types
• Union types
• Function types

Aggregate and Function Types

• Array types and structure types are referred to as aggregate types
• The type of a function specifies the function's return value

Integer Types Details

• The details of standard integer types include storage sizes and value ranges
  • Char = 1 byte
  • Unsigned char = 1 byte
  • Signed char = 1 byte
  • Int = 2 or 4 bytes
  • Unsigned int = 2 or 4 bytes
  • Short = 2 bytes
  • Unsigned short = 2 bytes
  • Long = 8 bytes
  • Unsigned long = 8 bytes

Variable Storage and the sizeof operator

• sizeof operator can be used to check variable size
• The expressions sizeof(type) yields the storage size of the object or type in bytes
• Variables are named storage areas
• Each variable in C has a specific type that determines the size, layout of memory, range of values, and operations
• Variable names have letters, digits, and underscores, must start with a letter or underscore, and are case-sensitive

Basic Variable Types

• char: - Typically a single octet(one byte). This is an integer type.
• int: Most natural size of integer for Machine
• float: A single-precision floating point value
• double: A double-precision floating point value
• void: Represents the absence of type

C Variable Definition

• A variable definition tells the compiler the type and amount of storage for the variable Datatype variablename_list;
• type must be a valid C data type including char, w_char, int, float, double, bool, or any user-defined object
• variable_list may consist of one or more identifier names separated by commas
• The line int i, j, k; declares and defines variables i, j, and k of type int
• Variables can be initialized with datatype variable_name = value;

Variable Declaration

• A variable declaration provides assurance to the compiler that there exists a variable with the given type and name so that the compiler can proceed for further compilation without requiring the complete detail about the variable
• A variable definition has its meaning at the time of compilation only, the compiler needs actual variable definition at the time of linking the program
• Variables with static storage duration are implicitly initialized with NULL if no initializer is provided

Initializing Static Variables in C

• Variables with static storage duration are implicitly initialized with NULL (all bytes have the value 0) if no initializer is used
• Otherwise the variables are undefined

C: Variable Declaration and Use

• Variable declaration lets the compiler know of a variable with a give name and type without needing complete details
• Variable declaration is useful when using multiple files
• The keyword extern declares a variable
• Variables can be declared multiple times but defined only once

Constants (Literals)

• Constants have fixed values that cannot be altered
• It can be of any basic data type like an integer, a float, a character, or a string
• Constants behave like variables, but their values cannot be modified post-definition

Integer Literals

• An integer literal can be decimal, octal, or hexadecimal
• Prefix: 0x or 0X (hexadecimal), 0 (octal), nothing (decimal)
• Suffix: U and L (unsigned and long)
• Suffix can be upper or lowercase

Floating-Point Literals

• Has an integer part, decimal point, fractional part, and exponent part
• Can be decimal or exponential
• Must include decimal point, exponent, or both in decimal form
• Must include integer part, fractional part, or both in exponential form
• Signed exponent introduced by e or E

Character Constants

• Character literals are in single quotes (e.g., 'x') and stored in a char type
• Can be a plain character (e.g., 'x'), an escape sequence (e.g., '\t'), or a universal character (e.g., '\u02C0')
• Characters with backslashes have special meanings (e.g., newline \n, tab \t)

String Literals

• String literals are enclosed in double quotes ""
• A string contains characters (plain, escape sequences, and universal)
• Long lines can be broken into multiple lines using string literals and separating them with white spaces
• All three forms are identical strings

Defining Constants in C

• There are two ways to define constants
• Using the #define preprocessor
• Using the const keyword

Using the #define Preprocessor

• The syntax to define constant is #define identifier value

Using the const Keyword

• Using the const keyword means you can declare a type for the constant
• The syntax is const type variable = value;

Operators in C

• Operators are symbols that instruct the compiler to perform mathematical or logical functions
• C provides:
• Arithmetic Operators
• Relational Operators
• Logical Operators
• Bitwise Operators
• Assignment Operators
• Misc Operators

Arithmetic Operators

• +: Adds two operands
• -: Subtracts the second operand from the first
• *: Multiplies both operands
• /: Divides numerator by de-numerator
• %: Modulus Operator
• ++: Increment operator
• --: Decrement operator

Relational Operators

• == Checks if the values of two operands are equal or not
• != Checks if the values of two operands are equal or not.
• > Checks if the value of left operand is greater than the value of right operand
• < Checks if the value of left operand is less than the value of right operand
• >= Checks if the value of left operand is greater than or equal to the value of right operand
• <= Checks if the value of left operand is less than or equal to the value of right operand