c++ pass by reference vs pass by value code example

Example 1: pass by value and pass by reference c++

#include <iostream>
using namespace std;

void by_value(int x) {
  x *= 2;
}

void by_reference(int &x) {
  x *= 2;
}

int main() {
  int a1 = 5, a2 = 5;

  cout << "Before: a1 = " << a1 << ", a2 = " << a2 << "\n";
  
  by_value(a1);
  by_reference(a2);

  cout << "After: a1 = " << a1 << ", a2 = " << a2 << "\n";

  return 0;
}

Example 2: copy by reference copy by value

main() {
      int i = 10, j = 20;
      swapThemByVal(i, j);
      cout << i << "  " << j << endl;     // displays 10  20
      swapThemByRef(i, j);
      cout << i << "  " << j << endl;     // displays 20  10
      ...
   }

   void swapThemByVal(int num1, int num2) {
      int temp = num1;
      num1 = num2;
      num2 = temp;
   }

   void swapThemByRef(int& num1, int& num2) {
      int temp = num1;
      num1 = num2;
      num2 = temp;
   }