C++ Program:

Example:

#include <iostream>
using namespace std;

int main() {
  int n1,n2,temp;
  cout<<"Enter 1st number: ";
  cin>>n1;
  cout<<"Enter 2nd number: ";
  cin>>n2;
  temp=n1;
  n1=n2;
  n2=temp;
  cout<<"After Swap"<<endl;
  cout<<"1st number :"<<n1<<"\n2nd number :"<<n2;
  return 0;
}

Output:

  Enter 1st number : 7
  Enter 2nd number : 15
  After Swap
  1st number : 15
  2nd number : 7

Here we are using 3rd variable (above code temp)

temp = n1;  //Insert 1st variable data into temp variable
n1 = n2;  //Insert 2st variable data into 1st variable
n2 = temp;  //Finally, Insert temp variable data into 2nd variable