PhP function counter

Question

I need a simple counter in php and I know, where the problem is, everytime when I start the function, $counter will jump again to 0. I don't know how to solve that.

if(empty($_POST["message-to-send"])){
    doSomething();
}

function doSomething(){
    $counter=0; 
    $messages = array(
       "message1",
       "message2",
       "message3",
       "message4",
       "message5"
    );

    echo $messages[$counter];
    $counter++;
    if($counter>count($messages)){
        echo "something";
    }
}

Answer 1

If you make the $counter a static variable it will maintain its value over many calls

function doSomething(){
    static $counter=0; 
    $messages = array(
                     "message1",
                     "message2",
                     "message3",
                     "message4",
                     "message5"
        );

    echo $messages[$counter];
    $counter++;
    if($counter>count($messages)){
        echo "something";
    }
}

doSomething();
doSomething();

RESULT:

message1
message2