Using an operator, you can manipulate the contents of one or more variables to produce a new value.
For example, the following code uses the addition operator ( + ) to add the values of $x and $y together to produce a new value:
echo $x + $y;
An operator is a symbol that manipulates one or more values, usually producing a new value.
An expression in PHP is anything that evaluates to a value.
The expression can be any combination of values, variables, operators, and functions.
In the preceding example, $x + $y is an expression.
Here are some more examples of expressions:
$x + $y + $z $x - $y $x 5 true gettype( $test_var )
The values and variables that are used with an operator are known as operands .