function submit_survey(form) {
    if (check_form()) {
        if (!form.submit()) {
            document.getElementById('question').style.display = "none";
            document.getElementById('thanks').style.display = "";
        }
    }
}

function check_form() {
    if (!radio_checked(document.survey_form.q1) || !radio_checked(document.survey_form.q2) || !radio_checked(document.survey_form.q3) || !radio_checked(document.survey_form.q4)) {
        alert("请回答所有问题");
	return false;
    }
    else if (document.survey_form.q2[9].checked && document.survey_form.q2_other.value == "") {
        alert("请填写第2题其他内容");
	return false;
    }
    else if (document.survey_form.q4[3].checked && document.survey_form.q4_other.value == "") {
        alert("请填写第4题其他内容");
	return false;
    }
    else if (document.survey_form.email.value == "") {
        alert("请填写邮箱，以便我们联系你，从而寄送奖品。");
	return false;
    }
    else {
        if (!check_email(document.survey_form.email.value)) {
	    alert("请填写有效邮箱地址，以便我们联系你，从而寄送奖品。");
	    return false;
	}
	else {
	    return true;
	}
    }
}

function radio_checked(radio_group) {
    for (var i = 0; i < radio_group.length; i++) {
        if (radio_group[i].checked)
	    return true;
    }
    return false;
}

function check_email(email) {
    var reg_exp = /^[a-z][\w\-\.]*@[\w\.]+\.[a-z]{2,3}/i;
    return reg_exp.test(email);
}