How to make the button ID a variable to use in php?

Question

I am trying to set the ID as a variable, how can i?

<?php
    $counter = 1;
    $i = 1;
    $testvar[$i] = ("NUMBER" + $i);
?>
<input type="button" id="<?php echo($testvar[$i]); ?>"/>
<script>
    var btn['<?php echo($i); ?>'] = document.getElementById("<?php echo($testvar[$i]); ?>");
    btn.onclick = CreateButton;
    function CreateButton(){
    <?php
        $counter++;
        while ($i < $counter){
            i++;
            echo("<input type='button' id='<?php echo($testvar[$i]); ?>'/>");
        }        
    ?>
};
</script>

The ID is not being reconigzed as a variable

Answer 1

You forgot to add the $ to one of our variables:

<?php
    $counter++;
    while ($i < $counter){
        $i++; //Missing $
        echo("<input type='button' id='<?php echo($testvar[$i]); ?>'/>");
    }        
?>

And as a sidenote, your question is really unclear. You should describe better what is not working.