std::numbers

C++20 introduced mathematical constants via the <numbers> header.

For example, we can compute the area of a circle, using the value of \(\pi\) from this library:

Listing 10 circle.cpp

#include <iostream>
#include <numbers>

int main() {

    double r{2.0};

    // we'll compute r**2 as r * r
    double area = std::numbers::pi * r * r;

    std::cout << "area = " << area << std::endl;

}

Important

By default, the compilers we are using assume C++17 as the standard. For access to the <numbers> library, we need to tell the compiler to use the C++20 standard. We do this by adding -std=c++20 to the compile line, e.g.:

g++ -std=c++20 -o circle circle.cpp