First C Program and its Structure

Lets see how to write a simple and most basic C program:

#include <stdio.h>
int main()
{
 printf("Hello,World");  //single line comment
 return 0;
/*
    multi
    line
    comments
/*
}

Hello,World


Different parts of C program

  • Pre-processor
  • Header file
  • Function
  • Variables
  • Statements & expressions
  • Comments

All these are essential parts of a C language program.


Pre-processor

#include is the first word of any C program. It is also known as a pre-processor. The task of a pre-processor is to initialize the environment of the program, i.e to link the program with the header files required.

So, when we say #include <stdio.h>, it is to inform the compiler to include the stdio.h header file to the program before executing it.


Header file

A Header file is a collection of built-in(readymade) functions, which we can directly use in our program. Header files contain definitions of the functions which can be incorporated into any C program by using pre-processor #include statement with the header file. Standard header files are provided with each compiler, and covers a range of areas like string handling, mathematical functions, data conversion, printing and reading of variables.

With time, you will have a clear picture of what header files are, as of now consider as a readymade piece of function which comes packaged with the C language and you can use them without worrying about how they work, all you have to do is include the header file in your program.

To use any of the standard functions, the appropriate header file must be included. This is done at the beginning of the C source file.

For example, to use the printf() function in a program, which is used to display anything on the screen, the line #include <stdio.h> is required because the header file stdio.h contains the printf() function. All header files will have an extension .h


main() function

main() function is a function that must be there in every C program. Everything inside this function in a C program will be executed. In the above example, int written before the main() function is the return type of main() function. we will discuss about it in detail later. The curly braces { } just after the main() function encloses the body of main() function.

We will learn what functions are in upcoming tutorials.


Comments

We can add comments in our program to describe what we are doing in the program. These comments are ignored by the compiler and are not executed.

To add a single line comment, start it by adding two forward slashses // followed by the comment.

To add multiline comment, enclode it between /* .... */, just like in the program above.


Return statement - return 0;

A return statement is just meant to define the end of any C program.

All the C programs can be written and edited in normal text editors like Notepad or Notepad++ and must be saved with a file name with extension as .c

If you do not add the extension .c then the compiler will not recognise it as a C language program file.


Writing your first C Program

In the video below we have explained stepwise how to write your first C program, compile it and run it.