Structure of a C Program

Basic Structure of a C Program

#include <stdio.h>      // Header file

int main() {             // Main function
    printf("Hello");     // Program statement
    return 0;            // End of program
}

This structure stays the same in almost every C program you will write.

Parts of a C Program

1. Documentation Section (Comments)

This section contains comments that describe the program, author name, date, and purpose of the program.

/*
  Program: Simple Hello Program
  Author : Your Name
  Date   : 2025
*/

2. Link Section (Header Files)

Header files provide functions used in your program. Example:

• stdio.h → printf(), scanf()
• math.h → mathematical operations
• string.h → string functions

#include <stdio.h>
#include <math.h>

3. Global Declaration Section

Variables and functions declared outside the main() function are called global declarations.

int count = 0;     // Global variable

void demo();       // Function declaration

4. main() Function

This is the heart of the entire program. Execution starts from the main() function.

int main() {
    // Your code goes here
}

5. Variable Declaration Section

Inside the main(), variables must be declared before they are used.

int age;  
float salary;

6. Statement/Executable Section

This part contains actual instructions that the program runs.

printf("Welcome!");
age = 21;
salary = 15000.50;

7. User-Defined Functions (Optional)

Large programs often break tasks into different functions to make the code simpler.

void greet() {
    printf("Hello User!");
}

Flow of a C Program

Documentation  
↓  
Link Section  
↓  
Global Declarations  
↓  
main()  
↓  
Variables  
↓  
Statements  
↓  
User-defined Functions  

Complete Example

#include <stdio.h>

// Global Declaration
int number = 10;

// User-Defined Function
void display() {
    printf("Number: %d\n", number);
}

int main() {
    printf("This is a C Program Structure Example\n");
    display();
    return 0;
}

Practice Questions

1. Explain all sections of a C program.
2. Why is main() important in C?
3. What is the purpose of header files?
4. Write the basic structure of a C program.
5. Differentiate between global and local variables.

Practice Task