Example: Circle Area Calculator in C++

// Circle Area Calculator
#include <iostream> // Required for input/output operations
#include <cmath>    // Required for M_PI (if available) or pow() function

// Define PI as a constant for better precision and readability
// Alternatively, use M_PI from <cmath> or define as acos(-1.0)
const double PI = 3.14159265358979323846;

// Function to calculate the area of a circle
// It takes the radius (double) as input
// It returns the calculated area (double)
double calculateCircleArea(double radius) {
    // Step 1: Check for a valid radius
    if (radius < 0) {
        std::cout << "Error: Radius cannot be negative." << std::endl;
        return 0.0; // Return 0 or an error indicator for invalid radius
    }
    // Step 2: Apply the formula: Area = PI * radius * radius
    // We can use radius * radius or pow(radius, 2)
    double area = PI * radius * radius;
    return area; // Return the calculated area
}

int main() {
    // Step 1: Declare a variable to store the radius
    double radius;

    // Step 2: Prompt the user to enter the radius
    std::cout << "Enter the radius of the circle: ";

    // Step 3: Read the radius from user input
    std::cin >> radius;

    // Step 4: Call the function to calculate the area
    // Store the returned value in a variable
    double areaOfCircle = calculateCircleArea(radius);

    // Step 5: Display the result if the radius was valid
    if (radius >= 0) {
        std::cout << "The area of the circle is: " << areaOfCircle << std::endl;
    }

    return 0; // Indicate successful program execution
}