Simultaneously reassign values of two variables in c++

Question

Is there a way in C++ of emulating this python syntax

a,b = b,(a+b)

I understand this is trivially possible with a temporary variable but am curious if it is possible without using one?

Answer 1

You can use the standard C++ function std::exchange like

#include <utility>

//...

a = std::exchange( b, a + b );

Here is a demonstration program

#include <iostream>
#include <utility>

int main()
{
    int a = 1;
    int b = 2;

    std::cout << "a = " << a << '\n';
    std::cout << "b = " << b << '\n';

    a = std::exchange( b, a + b );

    std::cout << "a = " << a << '\n';
    std::cout << "b = " << b << '\n';
}

The program output is

a = 1
b = 2
a = 2
b = 3

You can use this approach in a function that calculates Fibonacci numbers.