Example: Geometry Calculator in C++

// Geometry Calculator
#include <iostream>
#include <cmath> // For M_PI and pow function

// Function to calculate area of a circle
double calculateCircleArea(double radius) {
    return M_PI * pow(radius, 2);
}

// Function to calculate circumference of a circle
double calculateCircleCircumference(double radius) {
    return 2 * M_PI * radius;
}

// Function to calculate area of a rectangle
double calculateRectangleArea(double length, double width) {
    return length * width;
}

// Function to calculate perimeter of a rectangle
double calculateRectanglePerimeter(double length, double width) {
    return 2 * (length + width);
}

// Function to calculate area of a triangle (base * height / 2)
double calculateTriangleArea(double base, double height) {
    return 0.5 * base * height;
}

// Function to calculate area of a square
double calculateSquareArea(double side) {
    return side * side;
}

// Function to calculate perimeter of a square
double calculateSquarePerimeter(double side) {
    return 4 * side;
}

int main() {
    int choice;
    double value1, value2;

    // Step 1: Display the main menu
    do {
        std::cout << "\n--- Geometry Calculator ---" << std::endl;
        std::cout << "1. Calculate Area of Circle" << std::endl;
        std::cout << "2. Calculate Circumference of Circle" << std::endl;
        std::cout << "3. Calculate Area of Rectangle" << std::endl;
        std::cout << "4. Calculate Perimeter of Rectangle" << std::endl;
        std::cout << "5. Calculate Area of Triangle" << std::endl;
        std::cout << "6. Calculate Area of Square" << std::endl;
        std::cout << "7. Calculate Perimeter of Square" << std::endl;
        std::cout << "0. Exit" << std::endl;
        std::cout << "Enter your choice: ";
        std::cin >> choice;

        // Step 2: Process user's choice using a switch statement
        switch (choice) {
            case 1: // Area of Circle
                std::cout << "Enter the radius of the circle: ";
                std::cin >> value1;
                if (value1 < 0) {
                    std::cout << "Radius cannot be negative." << std::endl;
                } else {
                    std::cout << "The area of the circle is: " << calculateCircleArea(value1) << std::endl;
                }
                break;
            case 2: // Circumference of Circle
                std::cout << "Enter the radius of the circle: ";
                std::cin >> value1;
                if (value1 < 0) {
                    std::cout << "Radius cannot be negative." << std::endl;
                } else {
                    std::cout << "The circumference of the circle is: " << calculateCircleCircumference(value1) << std::endl;
                }
                break;
            case 3: // Area of Rectangle
                std::cout << "Enter the length of the rectangle: ";
                std::cin >> value1;
                std::cout << "Enter the width of the rectangle: ";
                std::cin >> value2;
                if (value1 < 0 || value2 < 0) {
                    std::cout << "Length and width cannot be negative." << std::endl;
                } else {
                    std::cout << "The area of the rectangle is: " << calculateRectangleArea(value1, value2) << std::endl;
                }
                break;
            case 4: // Perimeter of Rectangle
                std::cout << "Enter the length of the rectangle: ";
                std::cin >> value1;
                std::cout << "Enter the width of the rectangle: ";
                std::cin >> value2;
                if (value1 < 0 || value2 < 0) {
                    std::cout << "Length and width cannot be negative." << std::endl;
                } else {
                    std::cout << "The perimeter of the rectangle is: " << calculateRectanglePerimeter(value1, value2) << std::endl;
                }
                break;
            case 5: // Area of Triangle
                std::cout << "Enter the base of the triangle: ";
                std::cin >> value1;
                std::cout << "Enter the height of the triangle: ";
                std::cin >> value2;
                if (value1 < 0 || value2 < 0) {
                    std::cout << "Base and height cannot be negative." << std::endl;
                } else {
                    std::cout << "The area of the triangle is: " << calculateTriangleArea(value1, value2) << std::endl;
                }
                break;
            case 6: // Area of Square
                std::cout << "Enter the side length of the square: ";
                std::cin >> value1;
                if (value1 < 0) {
                    std::cout << "Side length cannot be negative." << std::endl;
                } else {
                    std::cout << "The area of the square is: " << calculateSquareArea(value1) << std::endl;
                }
                break;
            case 7: // Perimeter of Square
                std::cout << "Enter the side length of the square: ";
                std::cin >> value1;
                if (value1 < 0) {
                    std::cout << "Side length cannot be negative." << std::endl;
                } else {
                    std::cout << "The perimeter of the square is: " << calculateSquarePerimeter(value1) << std::endl;
                }
                break;
            case 0:
                std::cout << "Exiting Geometry Calculator. Goodbye!" << std::endl;
                break;
            default:
                std::cout << "Invalid choice. Please try again." << std::endl;
        }
    } while (choice != 0); // Step 3: Loop until user chooses to exit

    return 0;
}