Example: Calculate Circle Area using Function in C

// Calculate Circle Area using Function
#include <stdio.h>

// Define PI as a constant for better precision and readability
#define PI 3.14159265359

// Function declaration: Declares a function named calculateCircleArea
// It takes one argument (radius of type double) and returns a double.
double calculateCircleArea(double radius);

int main() {
    double radius; // Variable to store the radius entered by the user
    double area;   // Variable to store the calculated area

    // Step 1: Prompt the user to enter the radius of the circle
    printf("Enter the radius of the circle: ");

    // Step 2: Read the radius value from the user
    // %lf is used for reading a double
    scanf("%lf", &radius);

    // Step 3: Call the calculateCircleArea function
    // Pass the user-provided radius to the function
    // Store the returned area in the 'area' variable
    area = calculateCircleArea(radius);

    // Step 4: Display the calculated area to the user
    // %.2f formats the double to two decimal places
    printf("The area of the circle with radius %.2f is: %.2f\n", radius, area);

    return 0; // Indicate successful program execution
}

// Function definition: Implements the logic for calculateCircleArea
// It takes 'r' (radius) as input
double calculateCircleArea(double r) {
    // Calculate area using the formula A = PI * r * r
    return PI * r * r;
}