How to use constant expressions in C++?

In C++, a constant expression is an expression whose value can be determined at compile time. Using constant expressions can optimize the program at compile time and improve performance. They can be defined using the keyword constexpr.

Here is an example:

#include <iostream>

constexpr int add(int a, int b) {
    return a + b;
}

int main() {
    constexpr int x = 5;
    constexpr int y = 10;
    constexpr int result = add(x, y);

    std::cout << "The result is: " << result << std::endl;

    return 0;
}

In the example above, the add function uses the constexpr keyword, indicating that it is a constant expression function. In the main function, x and y are defined as constant expressions, and result is also a constant expression whose value can be determined at compile time.

Using constant expressions can improve the efficiency and performance of a program, especially in cases where values need to be determined at compile time. Constant expressions are a useful tool in such scenarios.