References

A reference is an alias for an existing variable — unlike a pointer, it can't be NULL, can't be reassigned to refer to something else, and needs no * to use.

int x = 10;
int &ref = x;  // ref IS x, just under another name

ref = 20;
std::cout << x << std::endl; // 20 — x itself changed

void increment(int &n) {
    n++;
}

int main() {
    int value = 5;
    increment(value);
    std::cout << value << std::endl; // 6
    return 0;
}

This solves the exact same problem C used a pointer for (increment(int *p)), with simpler syntax at the call site — no &x needed when calling, and no *p needed inside the function.

Common mistakes

• Reaching for a pointer out of habit from C when a reference would be simpler and equally safe — use a reference whenever the argument can never legitimately be "no value at all."

Practice

Write a function void doubleIt(int &n) that doubles its argument in place.

void doubleIt(int &n) {
    n *= 2;
}