help in Php globa variables

I work on a project in PHP/MYSQL and ad i have a problem.
I can't modify a global variable value, for example:

<?php
$Globalvariable=5;

if(something){
$Globalvariable=3;
}
else
$Globalvariable=10;


display();


function display(){
global $Globalvariable;

echo "Global variable : ".$Globalvariable."<br";


}
?>


the result of these code it should be 3 or 10, but in my case is 5.
I wait for replay!
Thanks !