How to use math pi in cpp?

You can define and use the mathematical constant Pi (π) in C++ using the atan function.

Defining Pi in C++

Here's how you can define PI in C++:

const double PI = std::atan(1.0) * 4;

Explanation:

• const double PI: This declares a constant variable named PI of type double to store the value of Pi. Using const ensures that the value of Pi cannot be accidentally modified later in the program.
• std::atan(1.0): This calculates the arctangent of 1.0, which is π/4 radians. std::atan is part of the <cmath> library (or <math.h>).
• *` 4**: This multiplies the result ofstd::atan(1.0)` by 4, giving the full value of Pi.

Important Considerations:

• Static Initialization: The reference mentions that the initialization of PI using std::atan is not guaranteed to be static. This means that its value might not be computed at compile time on all compilers. However, compilers like G++ often handle math functions like atan as intrinsics, enabling compile-time computation. If truly static initialization is crucial, consider alternative approaches or compiler-specific attributes if available.

Example Usage

#include <iostream>
#include <cmath>

int main() {
    const double PI = std::atan(1.0) * 4;

    double radius = 5.0;
    double area = PI * radius * radius;

    std::cout << "The area of a circle with radius " << radius << " is: " << area << std::endl;

    return 0;
}

This example calculates the area of a circle using the defined PI constant.

Summary Table