Real time Celsius to Fahrenheit Conversion

<!DOCTYPE html>
<html>
<head>
    <script>
        function convert(unit){
        if (unit == "C")
            document.getElementById("f").value = document.getElementById("c").value * 1.8 + 32;
        else
            document.getElementById("c").value = (document.getElementById("f").value - 32) * 1.8;
        }
    </script>
</head>
<body>
Celsius:<input id = "c" onkeyup = "convert('C')">
Fahrenheit:<input id = "f" onkeyup="convert('F')">
</form>
</body>
</html>