Example: Area Calculator using Functions in C

// Area Calculator using Functions
#include <stdio.h>  // For printf, scanf
#include <math.h>   // For M_PI (pi constant)

// Function to calculate the area of a circle
// Parameters: radius (float)
// Returns: area of the circle (float)
float areaCircle(float radius) {
    return M_PI * radius * radius;
}

// Function to calculate the area of a square
// Parameters: side (float)
// Returns: area of the square (float)
float areaSquare(float side) {
    return side * side;
}

// Function to calculate the area of a rectangle
// Parameters: length (float), width (float)
// Returns: area of the rectangle (float)
float areaRectangle(float length, float width) {
    return length * width;
}

int main() {
    int choice;
    float radius, side, length, width;
    float resultArea;

    // Step 1: Display menu to the user
    printf("Enter the shape for which to calculate area:\n");
    printf("1. Circle\n");
    printf("2. Square\n");
    printf("3. Rectangle\n");
    printf("Enter your choice (1-3): ");
    scanf("%d", &choice);

    // Step 2: Process user's choice using a switch statement
    switch (choice) {
        case 1:
            printf("Enter the radius of the circle: ");
            scanf("%f", &radius);
            resultArea = areaCircle(radius); // Call the areaCircle function
            printf("Area of the circle with radius %.2f is: %.2f\n", radius, resultArea);
            break;
        case 2:
            printf("Enter the side length of the square: ");
            scanf("%f", &side);
            resultArea = areaSquare(side); // Call the areaSquare function
            printf("Area of the square with side %.2f is: %.2f\n", side, resultArea);
            break;
        case 3:
            printf("Enter the length of the rectangle: ");
            printf("Enter the width of the rectangle: ");
            scanf("%f", &length);
            scanf("%f", &width);
            resultArea = areaRectangle(length, width); // Call the areaRectangle function
            printf("Area of the rectangle with length %.2f and width %.2f is: %.2f\n", length, width, resultArea);
            break;
        default:
            printf("Invalid choice. Please enter a number between 1 and 3.\n");
            break;
    }

    return 0;
}