Example: Procedural Circle Area in C++

C
C++
C#
Java
Python
PHP
// Procedural Circle Area
#include <iostream>
#include <cmath> // For M_PI or custom PI definition

// Define PI if not available via cmath (e.g., older compilers or specific standards)
#ifndef M_PI
#define M_PI 3.14159265358979323846
#endif

double calculateCircleArea(double radius) {
    return M_PI * radius * radius;
}

int main() {
    double radius;
    std::cout << "Enter the radius of the circle: ";
    std::cin >> radius;

    if (radius < 0) {
        std::cout << "Radius cannot be negative." << std::endl;
    } else {
        double area = calculateCircleArea(radius);
        std::cout << "The area of the circle with radius " << radius << " is: " << area << std::endl;
    }

    return 0;
}