PHP - 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.

<?php
function swap($x, $y) {
  echo "Before Swap.\n";
  echo "x = $x \n";
  echo "y = $y \n";

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

  echo "After Swap.\n";
  echo "x = $x \n";
  echo "y = $y \n";
}

swap(10, 25);
?>

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.

<?php
function swap($x, $y) {
  echo "Before Swap.\n";
  echo "x = $x \n";
  echo "y = $y \n";

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

  echo "After Swap.\n";
  echo "x = $x \n";
  echo "y = $y \n";
}

swap(10, 25);
?>

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.

<?php
function swap($x, $y) {
  echo "Before Swap.\n";
  echo "x = $x \n";
  echo "y = $y \n";

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

  echo "After Swap.\n";
  echo "x = $x \n";
  echo "y = $y \n";
}

swap(10, 25);
?>

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.

<?php
function swap($x, $y) {
  echo "Before Swap.\n";
  echo "x = $x \n";
  echo "y = $y \n";

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

  echo "After Swap.\n";
  echo "x = $x \n";
  echo "y = $y \n";
}

swap(10, 25);
?>

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.