为总数增加价值

Question

我正在寻找一种将（折扣）和（数量）中的值加到我的总计中的方法。至于折扣部分，客户将需要输入正确的代码以接收折扣。对于数量，单击复选框然后更改数量，总计也将随之增加。你们能帮我解决这个问题吗？ 谢谢 （对不起，我的英语不好）

function addItemPrice() {
  var total = 0;
  var count = 0;
  for (var i = 0; i < document.myform.item.length; i++) {
    if (document.myform.item[i].checked) {
      total = (total + document.myform.item[i].value * 1); // another way to convert string to number
      count++;
    }
  }
  return total;
}


var sh_prices = new Array();
sh_prices["standard"] = 10;
sh_prices["express"] = 20;

function getAddShipping() {
  var shippingPrice = 0;
  var theForm = document.forms["myform"];
  var shipping = theForm.elements["shipping"]
  for (var i = 0; i < shipping.length; i++) {
    if (shipping[i].checked) {
      shippingPrice = sh_prices[shipping[i].value];
      break;
    }
  }
  return shippingPrice;
}

function getCode() {
  var theForm = document.forms["myform"];
  var discode = theForm.elements["discount"]
  if (discode == "UAC123") {
    alert("yes");
  } else {
    alert("no")
  }
}


function getTotal() {
  var totalPrice = getAddShipping() + addItemPrice();
  document.getElementById('Price').innerHTML = "the total price" + totalPrice;
}

<form name="myform">
  Sickle $5 <input type="checkbox" name="item" value="5" onclick="getTotal(item)">
  <input type="number" name="quantity"><br> Sickle $1 <input type="checkbox" name="item" value="1" onclick="getTotal(item)">
  <input type="number" name="quantity" value="1"><br> Sickle $50 <input type="checkbox" name="item" value="50" onclick="getTotal(item)">
  <input type="number" name="quantity" value="1"><br> Sickle $5 <input type="checkbox" name="item" value="5" onclick="getTotal(item)">
  <input type="number" name="quantity" value="1"><br> Sickle $7 <input type="checkbox" name="item" value="7" onclick="getTotal(item)">
  <input type="number" name="quantity" value="1"><br> Standard
  <input type="radio" name="shipping" value="standard" onClick="getTotal(shipping)" /> Express
  <input type="radio" name="shipping" value="express" onClick="getTotal(shipping)" /> <br> Discount code
  <input type="text" name="discount" size=15>
  <input type="button" id="code" value="check" onClick="getCode(code)">

  <div id="Price">
  </div>

</form>