function check_form(formId){
    var mail_attr = /^[a-zA-Z0-9\-.]+\@[a-zA-Z0-9 \-\.]+\.([a-zA-Z]{2,3})$/;
    var name_attr = /[^A-Za-z\d]/;
    if(formId == "register"){
        var name        = $('.name_string').val();
        var password    = $('.password_string').val();
        var mail        = $('.mail_string').val();
        var agb         = $('#agb_select:checked').attr('checked');
        
        var error       = "";
        
        if(name == "" || name_attr.test(name)){
            $('#name_error').show();
            $('.name_string').css('border-color', '#ff0000');
            error += "name ";
        }else{
            $('#name_error').hide();
            $('.name_string').css('border-color', '');
        }
        
        if(password == ""){
            $('#password_error').show();
            $('.password_string').css('border-color', '#ff0000');
            error += "password ";
        }else{
            $('#password_error').hide();
            $('.password_string').css('border-color', '');
        }
        
        if(mail == "" || !mail_attr.test(mail)){
            $('#mail_error').show();
            $('.mail_string').css('border-color', '#ff0000');
            error += "mail ";
        }else{
            $('#mail_error').hide();
            $('.mail_string').css('border-color', '');
        }
        
        if(!agb){
            $('#agb_span').css('color', '#ff0000');
            $('#agb_span').css('font-weight', 'bold');
            error += "agb ";
        }else{
            $('#agb_span').css('color', '');
            $('#agb_span').css('font-weight', '');
        }
        
        if(error != ""){
            return false;
        }        
    }
    
    if(formId == "einloesen"){
        var vorname     = $('.vorname_string').val();
        var nachname    = $('.nachname_string').val();
        var strasse     = $('.strasse').val();
        var nummer      = $('.smaller').val();
        var ort         = $('.ort').val();
        var plz         = $('.plz').val();
        
        var error       = "";
        
        if(vorname == ""){
            $('#vorname_error').show();
            $('.vorname_string').css('border-color', '#ff0000');
            error += "vorname ";
        }else{
            $('#vorname_error').hide();
            $('.vorname_string').css('border-color', '');
        }
        
        if(nachname == ""){
            $('#nachname_error').show();
            $('.nachname_string').css('border-color', '#ff0000');
            error += "nachname ";
        }else{
            $('#nachname_error').hide();
            $('.nachname_string').css('border-color', '');
        }
        
        if(ort != "" && plz != "" && !isNaN(plz)){
            $('#ort_error').hide();
            $('.ort').css('border-color', '');
            $('.plz').css('border-color', '');
        }else if(ort == "" || plz == "" || isNaN(plz)){
            $('#ort_error').show();
            $('.ort').css('border-color', '#ff0000');
            $('.plz').css('border-color', '#ff0000');
            error += "ort ";
        }
        
        if(strasse != "" && nummer != ""){
            $('#strasse_error').hide();
            $('.strasse').css('border-color', '');
            $('.smaller').css('border-color', '');
        }else if(strasse == "" || nummer == ""){
            $('#strasse_error').show();
            $('.strasse').css('border-color', '#ff0000');
            $('.smaller').css('border-color', '#ff0000');
            error += "strasse ";
        }
        
        if(error != ""){
            return false;
        }
    }
    
    if(formId == "loginForm"){
        var nick        = $('.loginname').val();
        var password    = $('.loginpassword').val();
        
        if(nick == "" || password == ""){
            $('.loginname').css('border', '1px solid');
            $('.loginname').css('border-color', '#ff0000');
            
            $('.loginpassword').css('border', '1px solid');
            $('.loginpassword').css('border-color', '#ff0000');
            
            return false;
        }
    }
    
    if(formId == "kontaktForm"){
        var name   = $('.name_string').val();
        var mail   = $('.mail_string').val();
        var betreff= $('.betreff_string').val();
        var message= $('.message_string').val();
        
        var error = "";
        
        if(name == ""){
            $('.name_string').css('border-color', '#ff0000');
            error += "name ";
        }else{
            $('.name_string').css('border-color', '');
        }
        
        if(mail == "" || !mail_attr.test(mail)){
            $('.mail_string').css('border-color', '#ff0000');
            error += "mail ";
        }else{
            $('.mail_string').css('border-color', '');
        }
        
        if(betreff == ""){
            $('.betreff_string').css('border-color', '#ff0000');
            error += "betreff ";
        }else{
            $('.betreff_string').css('border-color', '');
        }
        
        if(message == ""){
            $('.message_string').css('border-color', '#ff0000');
            error += "message ";
        }else{
            $('.message_string').css('border-color', '');
        }
        
        if(error != ""){
            return false;
        }
    }
    
    if(formId == "freunde"){
        var mail1   = $('.mail1_string').val();
        var mail2   = $('.mail2_string').val();
        var mail3   = $('.mail3_string').val();
        var error = "";
        
        if(!mail_attr.test(mail1)){
            $('.mail1_string').css('border-color', '#ff0000');
            error += "mail1 ";
        }else{
            $('.mail1_string').css('border-color', '');
        }
        
        if(!mail_attr.test(mail2)){
            $('.mail2_string').css('border-color', '#ff0000');
            error += "mail2 ";
        }else{
            $('.mail2_string').css('border-color', '');
        }
        
        if(!mail_attr.test(mail3)){
            $('.mail3_string').css('border-color', '#ff0000');
            error += "mail3 ";
        }else{
            $('.mail3_string').css('border-color', '');
        }
        
        if(error != "" || (mail1 == "" && mail2 == "" && mail3 == "")){
            return false;
        }
    }
    
    if(formId == "freunde"){
        var new_nickname   = $('.nick_string').val();
        var error = "";
        
        if(name_attr.test(new_nickname)){
            $('.nick_string').css('border-color', '#ff0000');
            error += "nickname ";
        }else{
            $('.nick_string').css('border-color', '');
        }
        
        if(error != ""){
            return false;
        }
    }
}