pass by value and pass by reference c 2b 2b

1#include <iostream>
2using namespace std;
3
4void by_value(int x) {
5  x *= 2;
6}
7
8void by_reference(int &x) {
9  x *= 2;
10}
11
12int main() {
13  int a1 = 5, a2 = 5;
14
15  cout << "Before: a1 = " << a1 << ", a2 = " << a2 << "\n";
16  
17  by_value(a1);
18  by_reference(a2);
19
20  cout << "After: a1 = " << a1 << ", a2 = " << a2 << "\n";
21
22  return 0;
23}