Swapping Values Using References

Swapping values using references without a temporary variable is a neat trick in C++. It's not only efficient but also demonstrates the power of references. Here's how you can do it:

1#include <iostream>
2
3void swap(int& a, int& b) {
4  a = a + b;
5  b = a - b;  // b is now original a
6  a = a - b;  // a is now original b
7}
8
9int main() {
10  int x{5};
11  int y{10};
12
13  std::cout << "Before swap: x = "
14    << x << ", y = " << y << '\n';
15  swap(x, y);
16  std::cout << "After swap:  x = "
17    << x << ", y = " << y << '\n';
18}

1Before swap: x = 5, y = 10
2After swap:  x = 10, y = 5

Let's break down how this works.

First, we define a swap() function that takes two integer references as parameters.

Then, inside swap(), we perform three operations:

• Add b to a, storing the result in a.
• Subtract the new b from a, which gives us the original value of a, and store it in b.
• Subtract the new b from a, which gives us the original value of b, and store it in a.

This method works because we're using references, so we're directly manipulating the original variables, not copies.

While this method is clever, it's worth noting that it can cause issues with overflow for very large numbers. In practice, the standard library's std::swap() function is often a better choice:

1#include <iostream>
2#include <utility>
3
4int main() {
5  int x{5};
6  int y{10};
7
8  std::cout << "Before swap: x = "
9    << x << ", y = " << y << '\n';
10  std::swap(x, y);
11  std::cout << "After swap:  x = "
12    << x << ", y = " << y << '\n';
13}

std::swap() is more versatile as it works with any type, not just integers, and it handles potential edge cases more robustly.