Pass by Value and Reference

void addOneCopy(int x) { x++; }      // changes a copy
void addOneRef(int &x) { x++; }      // changes the original

int main() {
    int a = 5;
    addOneCopy(a);
    cout << a << endl;  // 5
    addOneRef(a);
    cout << a << endl;  // 6
}