Neither is the correct answer. Pi is a constant, not a variable. In C++, it is defined in <numbers> in C++20, or commonly by M_PI in <math.h> / <cmath> (requires _USE_MATH_DEFINES in VC++, but not gnu or clang).
Here's an example of how to use M_PI in a C++ program:
#include <iostream>
#include <cmath>
using namespace std;
int main() {
// Calculate the area of a circle with radius 5
double radius = 5.0;
double area = M_PI * radius * radius;
// Print the result
cout << "The area of the circle is: " << area << endl;
return 0;
}
This program will output the following:
The area of the circle is: 78.5398