Different Between Double Quote & Single Quote

Different Between Double Quote & Single Quote :-

echo Function into Single Quote  into the print value of Variables And it is not possible into the Double Quote.

Syntax :-

<?php 

     echo '$variable_name';

     echo "$variable_name";

?>

• Above Syntax into the Second Statement Into Generate the Error because the double quote into not print the value of variable.

Example :-

<?php 

     $a=555;

     echo 'Value of the Variable $a';

     echo "Value of the Variable $a";

?>