Perimeter and Area of Circle

#include <iostream>
using namespace std;

int main() {
    cout << "Enter circle radius. r = ";
    double r;
    cin >> r;
    double pi = 3.14159265359;
    cout << "Area = " << pi * r * r << endl;
    cout << "Perimeter = " << 2 * pi * r << endl;

    return 0;
}