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C Program Basic Structure

Input and Output in C

In this lesson, we will look at how a basic structure of a C program looks like and what are the basic components of it.

Basic Structure of a C Program

Before we start learning how to write a program in C, let us first understand how a basic structure of a C program look likes.

c program structure


This is how a simple basic structure of a C program looks like.

#include <stdio.h>
#include <conio.h>

int main()

    return 0;

Now we will discuss the various parts of the basic structure of a C program given above.

Preprocessor Directive

The Preprocessor Directive begins with the character #. It is used to include the necessary header file in a C program before compilation.

Header File

The Header File contains the function declaration and macro definition for C in-built library functions which we use in our C program during programing. When we include header file in C program using #include <filename.h> command, all codes inside the header file is included in the C program and then the program is sent to the compiler for compilation.

Definition/Declaration Section

This section is used to define macro, structure and global variables to be used in the programs, that means you can use these variables throughout the program.

Program Main Function (Entry Point)

In C, the main function is treated as the entry point of the program, it has a return type (and in some cases accepts inputs via parameters). The main function is called by the operating system when the user runs the program.

Main Function Return Type

In the latest standard of C, int is used as the return type of the main function. It means that the C program on its successful completion will return a value which is of type int. The default value of the return type is 0 if the program execution is normal.

Opening Brace

This is called the Opening Brace {. Whatever we will write inside the main function, we will write it after the Opening Brace.

Body of Main Function

In this section, we will write our C program, which will be executed by the main function after compilation.

Main Function Return Value

The return value for main is used to indicate how the program exited. If the program execution is normal, a 0 return value is used. Abnormal termination(errors, invalid inputs, segmentation faults, etc.) is usually terminated by a non-zero return.

Closing Brace

This is called the Closing Brace }. We use the Closing Brace at the end of the program.

Function Definition Section

When we want to define our function that fulfills a particular requirement, we can define them in this section.

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