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Structure of a C Program

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Introduction

Before writing complex programs, it is important to understand how a C program is structured. Just like a building needs a proper design, a C program also follows a specific structure.

Understanding this structure helps you write clean, organized, and error-free code.

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Basic Structure of a C Program

A C program is generally divided into the following sections:

1. Documentation Section
2. Link Section
3. Definition Section
4. Global Declaration Section
5. Main Function
6. Subprograms (User-defined Functions)

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Simple Example Program

// Program to calculate area of circle

#include <stdio.h>

#define PI 3.14

int main() {
    int radius = 5;
    float area;

    area = PI * radius * radius;

    printf("Area of Circle = %f", area);

    return 0;
}

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Output

Area of Circle = 78.500000

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Detailed Explanation of Each Section

1. Documentation Section

• Contains comments about the program
• Helps others understand your code

👉 Example:

// Program to calculate area of circle

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2. Link Section

• Includes header files
• Provides predefined functions

👉 Example:

#include <stdio.h>

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3. Definition Section

• Defines constants using #define

👉 Example:

#define PI 3.14

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4. Global Declaration Section

• Declares global variables and functions
• Accessible throughout the program

👉 Example:

int x;

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5. Main Function (Heart of Program)

• Execution starts from main()
• Every C program must have it

👉 Example:

int main() {
    // code
}

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6. Subprograms (User-defined Functions)

• Functions created by the user
• Used for modular programming

👉 Example:

void display() {
    printf("Hello");
}

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Flow of Execution

👉 The program runs in this order:

1. Preprocessor directives
2. main() function
3. Other functions

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Important Rules to Remember

• ✔ Every program must have main()
• ✔ Statements end with ;
• ✔ Use proper indentation
• ✔ Include necessary header files

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Common Mistakes

• ❌ Missing #include <stdio.h>
• ❌ Incorrect main() syntax
• ❌ Forgetting return 0;
• ❌ Missing semicolons

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Pro Tips

• ✔ Write code in proper structure
• ✔ Use comments for clarity
• ✔ Break large programs into functions
• ✔ Practice writing structured programs

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Conclusion

Understanding the structure of a C program is essential for writing efficient and organized code. It forms the backbone of all C programs and helps you build strong programming skills.

Once you master this, writing complex programs becomes much easier.

👉 This article is part of Dharani Tech Edu Hub — where learning programming is made simple and practical.