Example: Calculate Area of Circle Using User-Defined Function in C

// Calculate Area of Circle Using User-Defined Function
#include <stdio.h> // Required for input/output operations

// Define the constant PI for calculations
const double PI = 3.14159;

// Function to calculate the area of a circle
// It takes a double 'radius' as input and returns the calculated area as a double.
double calculateCircleArea(double radius) {
    // Step 1: Calculate the area using the formula: Area = PI * radius * radius
    double area = PI * radius * radius;
    // Step 2: Return the calculated area
    return area;
}

int main() {
    // Step 1: Declare a variable to store the radius entered by the user
    double radius;
    // Step 2: Declare a variable to store the calculated area
    double area;

    // Step 3: Prompt the user to enter the radius
    printf("Enter the radius of the circle: ");
    // Step 4: Read the radius from the user input
    // Use %lf for reading double values
    scanf("%lf", &radius);

    // Step 5: Call the user-defined function to calculate the area
    // Pass the 'radius' to the function and store the returned value in 'area'
    area = calculateCircleArea(radius);

    // Step 6: Display the calculated area to the user
    // Use %.2lf to print the double value with two decimal places
    printf("The area of the circle with radius %.2lf is: %.2lf\n", radius, area);

    return 0; // Indicate successful program execution
}