PHP Program to Swap Two Numbers

In PHP, you can swap two numbers using a temporary variable like this: $temp = $a; $a = $b; $b = $temp; which exchanges the values of $a and $b.

Examples

Inputa = 5, b = 10

OutputAfter swap: a = 10, b = 5

Inputa = -3, b = 7

OutputAfter swap: a = 7, b = -3

Inputa = 0, b = 0

OutputAfter swap: a = 0, b = 0

How to Think About It

To swap two numbers, think of holding one number temporarily so you don't lose it when you overwrite its variable. Store the first number in a temporary place, assign the second number to the first variable, then put the temporary number into the second variable.

Algorithm

1

Get the first number and store it in a temporary variable.

2

Assign the second number's value to the first number's variable.

3

Assign the temporary variable's value to the second number's variable.

4

Print or return the swapped values.

Code

php

<?php
$a = 5;
$b = 10;

// Swap using a temporary variable
$temp = $a;
$a = $b;
$b = $temp;

echo "After swap: a = $a, b = $b";
?>

Output

After swap: a = 10, b = 5

Dry Run

Let's trace swapping a = 5 and b = 10 through the code

1

Store first number in temp

$temp = 5 (value of a)

2

Assign second number to first

$a = 10 (value of b)

3

Assign temp to second number

$b = 5 (value of temp)

Variable	Value
$temp	5
$a	10
$b	5

Why This Works

Step 1: Temporary storage

We use $temp to hold the value of $a so it is not lost when we overwrite $a.

Step 2: Overwrite first variable

We assign the value of $b to $a, so now $a has the second number.

Step 3: Restore second variable

We assign the stored value in $temp to $b, completing the swap.

Alternative Approaches

Swap without temporary variable using arithmetic

php

<?php
$a = 5;
$b = 10;

$a = $a + $b;
$b = $a - $b;
$a = $a - $b;

echo "After swap: a = $a, b = $b";
?>

This method avoids extra variable but can cause overflow with very large numbers.

Swap without temporary variable using list()

php

<?php
$a = 5;
$b = 10;

list($a, $b) = array($b, $a);

echo "After swap: a = $a, b = $b";
?>

This is a clean and readable PHP-specific way to swap values without a temp variable.

Complexity: O(1) time, O(1) space

Time Complexity

Swapping two numbers takes constant time because it involves only a fixed number of assignments.

Space Complexity

Using a temporary variable requires constant extra space, which is minimal and efficient.

Which Approach is Fastest?

All methods run in constant time; using list() is cleanest in PHP, while arithmetic swap avoids extra variables but risks overflow.

Approach	Time	Space	Best For
Temporary variable	O(1)	O(1)	Safe and clear swapping
Arithmetic swap	O(1)	O(1)	No extra variable but risk with large numbers
list() swap	O(1)	O(1)	Clean PHP syntax, readable