Structure of a C Program (6 Modular Sections)

Every robust C program follows a modular structure composed of 6 standard sections: documentation, link preprocessors, definitions, global declarations, main entry, and subprogram routines.

Understanding the modular architecture of C code ensures clean scoping, zero undefined behavior, and optimal standard C11/C17 compliance.

Review the standard 6-part layout below and run it in the compiler to inspect how macros, global states, and user functions execute.

Interactive Runnable C Implementation

/* ==========================================
   Section 1: Documentation Section
   Author: Online C Compiler Team
   Purpose: Demonstrate standard C program layout
   ========================================== */

// Section 2: Link / Preprocessor Directives
#include <stdio.h>
#include <stdbool.h>

// Section 3: Definition Section (Macros / Constants)
#define MAX_BUFFER 100
#define PI 3.14159

// Section 4: Global Declaration Section
int g_execution_count = 0;          // Global variable
void print_banner(const char *msg); // Function prototype

// Section 5: Main Function
int main(void) {
    g_execution_count++;
    
    char title[] = "Online C Compiler Architecture";
    print_banner(title);
    
    printf("Execution Count: %d\n", g_execution_count);
    printf("Max Buffer: %d | PI: %.5f\n", MAX_BUFFER, PI);
    
    return 0;
}

// Section 6: Subprogram / Function Definition Section
void print_banner(const char *msg) {
    printf("==============================\n");
    printf("%s\n", msg);
    printf("==============================\n");
}

Open example in compiler

Expected Output

==============================
Online C Compiler Architecture
==============================
Execution Count: 1
Max Buffer: 100 | PI: 3.14159