Variable manipulation is the process of modifying the value of a variable in PHP. PHP provides a wide range of operators and functions for variable manipulation, including arithmetic operators, string operators, and comparison operators.

Here are some examples of variable manipulation in PHP:

## 1. Arithmetic operators:

PHP provides arithmetic operators for performing basic mathematical operations on variables. These operators include addition (+), subtraction (-), multiplication (*), division (/), modulus (%), and exponentiation (**).

For example:

```
$num1 = 10;
$num2 = 5;
// Addition
$result = $num1 + $num2; // $result = 15
// Subtraction
$result = $num1 - $num2; // $result = 5
// Multiplication
$result = $num1 * $num2; // $result = 50
// Division
$result = $num1 / $num2; // $result = 2
// Modulus
$result = $num1 % $num2; // $result = 0
// Exponentiation
$result = $num1 ** $num2; // $result = 100000
```

## 2. String operators:

PHP provides string operators for manipulating strings. These operators include concatenation (.), concatenation assignment (.=), and substring (substr()).

For example:

```
$str1 = "Hello";
$str2 = "world";
// Concatenation
$result = $str1 . " " . $str2; // $result = "Hello world"
// Concatenation assignment
$str1 .= " PHP"; // $str1 = "Hello PHP"
// Substring
$result = substr($str1, 0, 5); // $result = "Hello"
```

## 3. Comparison operators:

PHP provides comparison operators for comparing variables. These operators include equal to (==), not equal to (!=), identical to (===), not identical to (!==), greater than (>), less than (<), greater than or equal to (>=), and less than or equal to (<=).

For example:

```
$num1 = 10;
$num2 = 5;
// Equal to
$result = ($num1 == $num2); // $result = false
// Not equal to
$result = ($num1 != $num2); // $result = true
// Identical to
$result = ($num1 === $num2); // $result = false
// Greater than
$result = ($num1 > $num2); // $result = true
// Less than
$result = ($num1 < $num2); // $result = false
// Greater than or equal to
$result = ($num1 >= $num2); // $result = true
// Less than or equal to
$result = ($num1 <= $num2); // $result = false
```