how to use #define c++
#include <iostream>
#define PI 3.14159
#define SQUARE(x) ((x)*(x))
int main() {
double radius = 5.0;
double area = PI * SQUARE(radius);
std::cout << "Radius: " << radius << std::endl;
std::cout << "Area: " << area << std::endl;
return 0;
}