Example: Area Calculator using Functions in C

// Area Calculator using Functions
#include <stdio.h>
#include <math.h> // Required for M_PI (Pi value)

// Function to calculate the area of a circle
// Takes the radius as input and returns the area
double calculateCircleArea(double radius) {
    return M_PI * radius * radius;
}

// Function to calculate the area of a rectangle
// Takes length and width as input and returns the area
double calculateRectangleArea(double length, double width) {
    return length * width;
}

// Function to calculate the area of a triangle
// Takes base and height as input and returns the area
double calculateTriangleArea(double base, double height) {
    return 0.5 * base * height;
}

int main() {
    // Step 1: Declare variables for inputs and results
    double radius, length, width, base, height;
    double circleArea, rectangleArea, triangleArea;

    // Step 2: Get user input for circle and calculate its area
    printf("--- Circle Area Calculation ---\n");
    printf("Enter the radius of the circle: ");
    scanf("%lf", &radius);
    circleArea = calculateCircleArea(radius); // Call the function
    printf("Area of the circle: %.2f\n\n", circleArea);

    // Step 3: Get user input for rectangle and calculate its area
    printf("--- Rectangle Area Calculation ---\n");
    printf("Enter the length of the rectangle: ");
    scanf("%lf", &length);
    printf("Enter the width of the rectangle: ");
    scanf("%lf", &width);
    rectangleArea = calculateRectangleArea(length, width); // Call the function
    printf("Area of the rectangle: %.2f\n\n", rectangleArea);

    // Step 4: Get user input for triangle and calculate its area
    printf("--- Triangle Area Calculation ---\n");
    printf("Enter the base of the triangle: ");
    scanf("%lf", &base);
    printf("Enter the height of the triangle: ");
    scanf("%lf", &height);
    triangleArea = calculateTriangleArea(base, height); // Call the function
    printf("Area of the triangle: %.2f\n\n", triangleArea);

    return 0;
}