function checkRequiredFields(input)
{

    var requiredFields = new Array("firstname",
                                   "surname",
                                   "street",
                                   "streetnumber",
                                   "zip",
                                   "city",
                                   "telnocode",
                                   "telno",
                                   "email");

    var fieldNames = new Array("Vorname",
                               "Nachname",
                               "Straße",
                               "Hausnummer",
                               "Postleitzahl",
                               "Ort",
                               "Vorwahl",
                               "Telefonnummer",
                               "Emailadresse");
    var fieldCheck   = true;
    var fieldsNeeded = "\nIn diesem Formular müssen Sie alle Felder ausfüllen! \n Bitte füllen Sie folgende noch leere Felder aus:\n\n\t";

    for(var fieldNum=0; fieldNum < requiredFields.length; fieldNum++) {
        if ((input.elements[requiredFields[fieldNum]].value == "") ||
            (input.elements[requiredFields[fieldNum]].value == " ")) {

            fieldsNeeded += fieldNames[fieldNum] + "\n\t";
            fieldCheck = false;
        }
    }

    if (fieldCheck == true)
    {
        return true;
    }
    else
    {
        alert(fieldsNeeded);
        return false;
    }
}