Pass by Value vs. Pass by Reference

How Arguments Are Passed

By default C++ copies arguments — changes inside the function don't affect the original:

void doubleIt(int x) { x *= 2; }  // only changes local copy

int n = 5;
doubleIt(n);
cout << n;   // still 5!

Pass by reference — modify the original

Add & after the type to make it a reference:

void doubleIt(int& x) { x *= 2; }  // modifies the original

int n = 5;
doubleIt(n);
cout << n;   // 10

Return multiple values via out-parameters

void minMax(int a, int b, int c, int& mn, int& mx) {
    mn = min({a, b, c});
    mx = max({a, b, c});
}
int lo, hi;
minMax(3, 1, 7, lo, hi);  // lo=1, hi=7

Your Task

Write swap(int& a, int& b) that swaps two values in-place using a temporary variable.