function show() {
    var obj = document.getElementById('menu');
    var bul = document.getElementById('bul');
    if(obj.style.display == 'block') {
        obj.style.display = 'none';
        bul.innerHTML = '▼';
    } else {
        obj.style.display = 'block';
        bul.innerHTML = '▲';
    }
}

function checkValue(el) {
    var obj = document.getElementById(el);
    var error = document.getElementById(el+'_error');
    if(obj.value == '') {
        error.style.display = 'inline';
        return false;
    } else {
        error.style.display = 'none';
        return true;
    }
}

function checkEmail(el) {
    var obj = document.getElementById(el);
    var error = document.getElementById(el+'_error');
    if (obj.value != '') {
        var emailPat = /^([A-Za-z0-9_\-\.])+\@([A-Za-z0-9_\-\.])+\.([A-Za-z]{2,4})$/;
        emailStr = obj.value;
        var matchArray=emailStr.match(emailPat);
        if (matchArray==null) {
            error.style.display = 'inline';
            return false;
        } else {
            error.style.display = 'none';
            return true;
        }
    } else {
        error.style.display = 'inline';
        return false;
    }
}