Explain the different sections in C language

A C program follows a structured format with different sections that serve specific purposes. Understanding these sections helps in writing well-organized and maintainable code.

Structure of a C Program

The complete C program is divided into different sections, which are as follows −

• Documentation Section − Contains comments about the program like author name, creation or modification date. Information written between /* */ or after // is called a comment line. These lines are ignored by the compiler during compilation.

• Preprocessor Directives Section − In this section, header files required to execute the program are included using #include directive.

• Global Declaration Section − Here, global variables and symbolic constants are defined which can be used throughout the program.

• Function Prototype Declaration Section − This section declares function prototypes that specify return type, function name, and parameters without the actual function body.

• Main Function − The C program execution starts from this section. It contains local declarations and executable statements.

• User Defined Function Section − Users can define their own functions to perform specific tasks as per requirements.

Syntax

/* Documentation section */
#include <header_files>

/* Global declarations */
datatype global_variables;

/* Function prototypes */
return_type function_name(parameters);

int main() {
    /* Local declarations */
    datatype local_variables;
    
    /* Executable statements */
    statements;
    
    return 0;
}

/* User defined functions */
return_type function_name(parameters) {
    /* Local declarations */
    /* Executable statements */
    return value;
}

Example: Complete C Program Structure

Following is a C program demonstrating all sections with a function to perform addition −

/* Documentation Section
   Program: Addition of two numbers
   Author: Tutorial Example
   Date: 2024 */

#include <stdio.h>

/* Global Declaration Section */
int result;

/* Function Prototype Declaration */
void sum(int, int);

/* Main Function */
int main() {
    /* Local Declaration */
    int a, b;
    
    /* Reading User Input */
    printf("Enter two numbers: ");
    scanf("%d %d", &a, &b);
    
    /* Function Calling */
    sum(a, b);
    
    return 0;
}

/* User Defined Function Section */
void sum(int x, int y) {
    /* Local Declaration */
    int add;
    
    /* Addition Operation */
    add = x + y;
    
    /* Printing Output */
    printf("Addition of %d and %d is %d<br>", x, y, add);
}

Enter two numbers: 5 6
Addition of 5 and 6 is 11

Key Points

• The main() function is mandatory and serves as the entry point of the program.
• Documentation helps in code maintenance and understanding.
• Function prototypes must be declared before use or defined before the main function.
• Global variables are accessible throughout the program, while local variables are limited to their scope.

Conclusion

Understanding the structure of a C program with its different sections is fundamental for writing organized code. Each section has a specific purpose that contributes to the overall functionality and readability of the program.