sign.html: reports sign of number

<script>
    var num = prompt("Enter number")
    while (num != null) {
        num = parseInt(num)
    	if (num > 0) {
            alert(num + " is positive")
        } else if (num < 0) {
            alert(num + " is negative")
        } else {
            alert(num + " is zero")
        }
    	num = prompt("Enter number")
    }
</script>