function prazdnyInput(name){
        var obj = document.getElementById(name);
        var obj_er = document.getElementById('error_' + name);
	var out = '';
	for (var cnt = 0; cnt < obj.value.length; cnt++) {
		if (obj.value.charAt(cnt) != ' ') { out += obj.value.charAt(cnt); }
	}
        if (out.length < 1 ) {
	
        	obj.focus(); 
		obj_er.style.display = 'block';
		obj_er.style.color = 'red';
		return false;
	}
	obj_er.style.display = 'none';
	return true;
}
function checkEmail() {
        var obj = document.getElementById('email');
        var obj_er = document.getElementById('error_email_valid');
        var filter = /^([a-zA-Z0-9_\.\-])+\@(([a-zA-Z0-9\-])+\.)+([a-zA-Z0-9]{2,4})+$/;
        if (!filter.test(obj.value)) {
                obj.focus;
                obj_er.style.display = 'block';
                obj_er.style.color = 'red';
                return false;
        }
        obj_er.style.display = 'none';
        return true;
}
function captcha()
    {
        document.write("Kontrolní kód: </td>");
        document.write("<td>"+ a + " + " + b +" = <input id='kod' type='text' maxlength='2' size='2' /><span id='error_kod' style='display:none'>Špatný kontrolní kód!</span>");
    }    
function kontrolaCaptcha(){
        var obj = document.getElementById('kod'); 
        var obj_er = document.getElementById('error_kod');
        var d = obj.value;
        if (d != c) {
                obj.focus;
                obj_er.style.display = 'block';
                obj_er.style.color = 'red';
                return false;
                }        
        else{
                obj_er.style.display = 'none';
                return true;
        }
        
    }
function kontrola() {
        var chyba = false;
        
        if(!kontrolaCaptcha()){
                chyba = true;
        }
        if(!prazdnyInput('message')){
                chyba = true;
        }
        if(!prazdnyInput('email')){
                chyba = true;
        }
        if(!checkEmail('email')){
                chyba = true;
        }
        if(!prazdnyInput('name')){
                chyba = true;
        }
        if (chyba){
        	return false;
        }
        return true;
}