Swap Two Numbers

Swapping is the classic "hold one in your hand" problem. Two values can't occupy one variable, so the usual approach parks one of them in a temporary variable:

int t = a; a = b; b = t;

Two puzzle variants avoid the temporary:

• Arithmetic: a = a + b; b = a - b; a = a - b; (risks overflow)
• XOR: a ^= b; b ^= a; a ^= b; (fails if a and b are the same memory location)

Modern languages also offer destructuring: [a, b] = [b, a] in JS and a, b = b, a in Python.