I suppose that this is very noob question but I can't figure it out.

I've got code: 

```
for($i=1; $i<9; $i++){

    if (isset($_POST['is'$i'ID'])) {
        echo $i . " is OK<br>"; 
    }

}

```

And I know that the problem lies in this line : 

```
if (isset($_POST['is'$i'ID']))

```

How can I use variable i in this code?