C Programming : Introduction and Examples

 Introduction

 C Programming is a general-purpose, procedural, imperative computer programming language developed in 1972 by Dennis M. Ritchie. It was mainly developed as a system programming language to write an operating system.

The main features of the C language are

1.  low-level memory access
2.  a simple set of keywords
3. a clean style

These features make C language suitable for system programming like an operating system or compiler development. 

Structure of a C program 

Structure means that any program can be written in this structure only. Writing a C program in any other structure will lead to a Compilation Error.
The structure of a C program is as follows:

#include <stdio.h>	Header
int main( )	Main
{ int a=5	Variable declaration
printf("%d", a);	Body
return 0;	Return
}

 

The components of the above structure are: 

Header Files Inclusion:

 The first and foremost component is the inclusion of the Header files in a C program. 

A header file is a file with extension .h which contains C function declarations and macro definitions to be shared between several source files.

Some of C Header files are

stdio.h – Defines core input and output functions

stddef.h – Defines several useful types and macros.

stdint.h – Defines exact width integer types.

stdlib.h – Defines numeric conversion functions, pseudo-random network generator, memory allocation

string.h – Defines string handling functions

math.h – Defines common mathematical functions

Main Method Declaration

The next part of a C program is to declare the main() function. The syntax to declare the main function is:

Syantax

int main()

{

}

Variable Declaration: 

The next part of any C program is the variable declaration. It refers to the variables that are to be used in the function. In C programming, no variable can be used without being declared. Also in a C program, the variables are to be declared before any operation in the function.
Example

int main()

{

    int a;

} 

Body: 

The body of a function in the C program, refers to the operations that are performed in the functions. It can be anything like manipulations, searching, sorting, printing, etc.
Example

int main()

{

    int a;

    printf("%d", a);

} 

Return Statement

The last part of any C program is the return statement. The return statement refers to the returning of the values from a function. This return statement and return value depend upon the return type of the function. If the return type is void, then there will be no return statement. In any other case, there will be a return statement and the return value will be of the type of the specified return type.
Example

int main()

{

    int a;

    printf("%d", a);

    return 0;

}

 Example 1:

#include <stdio.h> int main(void) {     printf("Lbm4");     return 0; }

Now we will analyze the program line by line. 

Line 1: [ #include <stdio.h> ]

 In a C program, all lines that start with # are processed by a preprocessor which is a program invoked by the compiler. In a very basic term, the preprocessor takes a C program and produces another C program. The produced program has no lines starting with #, all such lines are processed by the preprocessor. In the above example 1 the preprocessor copies the preprocessed code of stdio.h to our file. The .h files are called header files in C. These header files generally contain declarations of functions. We need stdio.h for the function printf() used in the program. 

Line 2 [ int main(void) ]

 There must be a starting point from where execution of compiled C program begins. In C, the execution typically begins with the first line of main(). The void written in brackets indicates that the main doesn’t take any parameter. The int was written before main indicates return type of main(). The value returned by main indicates the status of program termination.

Line 3 and 6: [ { and } ] In C language, a pair of curly brackets define scope and are mainly used in functions and control statements like if, else, loops. All functions must start and end with curly brackets. 

Line 4 [ printf(“GeeksQuiz”); ]

 Printf() is a standard library function to print something on standard output. The semicolon at the end of printf indicates line termination. In C, a semicolon is always used to indicate end of a statement. 

Line 5 [ return 0; ] 

The return statement returns the value from main(). The returned value may be used by an operating system to know the termination status of your program. The value 0 typically means successful termination.