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C++ - Swap two numbers without using Temporary Variable



The value of two variables can be swapped without using any temporary variables. The method involves using operators like +, *, / and bitwise.

Method 1: Using + operator

In the example below, the + operator is used to swap the value of two variables x and y.

#include <iostream>
using namespace std;

static void swap(int, int);

static void swap(int x, int y) {
  cout<<"Before Swap.\n";
  cout<<"x = "<<x<<"\n";
  cout<<"y = "<<y<<"\n";

  //Swap technique
  x = x + y;
  y = x - y;
  x = x - y;

  cout<<"After Swap.\n";
  cout<<"x = "<<x<<"\n";
  cout<<"y = "<<y<<"\n";
}

int main() {
  swap(10, 25);
  return 0;
}

The above code will give the following output:

Before Swap.
x = 10
y = 25
After Swap.
x = 25
y = 10

Method 2: Using * operator

Like + operator, the * operator can also be used to swap the value of two variables x and y.

#include <iostream>
using namespace std;

static void swap(int, int);

static void swap(int x, int y) {
  cout<<"Before Swap.\n";
  cout<<"x = "<<x<<"\n";
  cout<<"y = "<<y<<"\n";

  //Swap technique
  x = x * y;
  y = x / y;
  x = x / y;

  cout<<"After Swap.\n";
  cout<<"x = "<<x<<"\n";
  cout<<"y = "<<y<<"\n";
}

int main() {
  swap(10, 25);
  return 0;
}

The above code will give the following output:

Before Swap.
x = 10
y = 25
After Swap.
x = 25
y = 10

Method 3: Using / operator

Similarly / operator can also be used to swap the value of two variables x and y.

#include <iostream>
using namespace std;

static void swap(float, float);

static void swap(float x, float y) {
  cout<<"Before Swap.\n";
  cout<<"x = "<<x<<"\n";
  cout<<"y = "<<y<<"\n";

  //Swap technique
  x = x / y;
  y = x * y;
  x = y / x;

  cout<<"After Swap.\n";
  cout<<"x = "<<x<<"\n";
  cout<<"y = "<<y<<"\n";
}

int main() {
  swap(10, 25);
  return 0;
}

The above code will give the following output:

Before Swap.
x = 10
y = 25
After Swap.
x = 25
y = 10

Method 4: Using bitwise operator

The bitwise XOR (^) operator can also be used to swap the value of two variables x and y. It returns 1 when one of two bits at same position in both operands is 1, otherwise returns 0.

#include <iostream>
using namespace std;

static void swap(int, int);

static void swap(int x, int y) {
  cout<<"Before Swap.\n";
  cout<<"x = "<<x<<"\n";
  cout<<"y = "<<y<<"\n";

  //Swap technique
  x = x ^ y;
  y = x ^ y;
  x = x ^ y;

  cout<<"After Swap.\n";
  cout<<"x = "<<x<<"\n";
  cout<<"y = "<<y<<"\n";
}

int main() {
  swap(10, 25);
  return 0;
}

The above code will give the following output:

Before Swap.
x = 10
y = 25
After Swap.
x = 25
y = 10

Disadvantages of using above methods

  • The multiplication and division based approaches fail if the value of one of the variable is 0.
  • The addition based approach may fail due to arithmetic overflow. If x and y are too large, operation performed on operands may result into out of range integer.



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