PHP Function call by value and call by reference

 <?php  

function increment($i)  

{  

    $i++;  

}  

$i = 10;  

increment($i);  

echo $i;  

?>

above function output is 10 

Call by Reference - 

<?php  

function adder(&$str2)  

{  

    $str2 .= 'Call By Reference';  

}  

$str = 'This is ';  

adder($str);  

echo $str;  

?>

above returns output is 'this is call by reference'

use & (ampersand) symbol with formal arguments. The & represents reference of the variable.