Lesson 4: Basic Structure of a C Program

Understanding the standard components of a C file is crucial for organization.

Key Components

A typical C program structure can be broken down into these parts:

1. Documentation Section: Comments describing the program, author, and date.
2. Preprocessor Directives: Lines starting with # (e.g., #include, #define).
3. Global Declarations: Variables or functions declared outside of any function.
4. The main() Function: Where execution begins.
5. User-Defined Functions: Functions written by the programmer to perform specific tasks.

Example Structure

c /* 1. Documentation: Program to calculate area */

// 2. Preprocessor Directive #include <stdio.h>

// 3. Global Declaration #define PI 3.14159

// 5. Function Prototypes (Declarations) float calculate_area(float radius);

// 4. Main Function int main() { float r = 5.0; float area = calculate_area(r); printf("Area: %f\n", area); return 0; }

// 5. Function Definition float calculate_area(float radius) { return PI * radius * radius; }

The Role of main()

The main function is mandatory. Its structure is standardized:

• int main(): The simplest form.
• int main(void): Explicitly states it takes no arguments.
• int main(int argc, char *argv[]): Used for handling command-line arguments (covered later).

Always ensure your main function returns an integer (usually 0 for success).