Example: Circle Area and Circumference Calculator in C++

// Circle Area and Circumference Calculator
#include <iostream> // Required for input/output operations
#include <cmath>    // Required for M_PI if using it, though we'll define our own PI for clarity

// Define PI as a constant for accurate calculations
// Using a double for precision
const double PI = 3.14159;

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

// Function to calculate the circumference of a circle
// Takes the radius as input and returns the circumference
double calculateCircumference(double radius) {
    return 2 * PI * radius;
}

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 the user
    std::cin >> radius;

    // Step 4: Call the calculateArea function and store the result
    double area = calculateArea(radius);

    // Step 5: Call the calculateCircumference function and store the result
    double circumference = calculateCircumference(radius);

    // Step 6: Display the calculated area
    std::cout << "The area of the circle is: " << area << std::endl;

    // Step 7: Display the calculated circumference
    std::cout << "The circumference of the circle is: " << circumference << std::endl;

    return 0; // Indicate successful program execution
}