how to concatenate variable in php code example

Example 1: php concatenate and add

this is inside for or foreach loop

# For concatenate use           .=
 $var .= 'string';

 # For adding the VALUES use    +=
 $var += 1;

Example 2: php concatenate two variables

$string = "the color is ";
$string .= "red";

echo $string; // gives: the color is red