include iostream include math using namespace std double area double r

#include <iostream>
#include <math.h>

using namespace std;

double area(double r) {
    return M_PI * pow(r, 2);
}

int main() {
    double r;

    cout << "Enter the radius of the circle: ";
    cin >> r;
    cout << "The area of a circle with a radius of " << r << " is equal to: " << area(r) << endl;

    return 0;
}