Как добавить функцию обработки десятичных дробей в калькулятор?

var num1;
var op;

function pressBtn(value) {
  var prev = document.forms["calc"]["display"].value;
  if (!(prev == "" && value == 0)) {
    var newval = prev + value;
    document.forms["calc"]["display"].value = newval;
  }

}

function pressOP(operator) {
  op = operator;
  var display = document.forms["calc"]["display"].value;
  num1 = parseInt(display);
  document.forms["calc"]["display"].value = "";
}

function pressEq() {
  var display = document.forms["calc"]["display"].value;
  var num2 = parseInt(display);
  switch (op) {

    case "+":
      var ans = num1 + num2;
      break;

    case "-":
      var ans = num1 - num2;
      break;

    case "*":
      var ans = num1 * num2;
      break;

    case "/":
      var ans = num1 / num2;
      break;

    case "^":
      var ans = Math.pow(num1, num2);
      break;

    case ".":
      var ans = ".";
      break;

    case "C":
      var ans = "";
      break;
  }
  document.forms["calc"]["display"].value = ans;
}

<div style=" text-align: center">
  <form name="calc">
    <input type="text" name="display" readonly><br>
    <input type="button" name="btn9" value="9" onClick="pressBtn(9)">
    <input type="button" name="btn8" value="8" onClick="pressBtn(8)">
    <input type="button" name="btn7" value="7" onClick="pressBtn(7)">
    <input type="button" name="btn6" value="6" onClick="pressBtn(6)"><br>
    <input type="button" name="btn5" value="5" onClick="pressBtn(5)">
    <input type="button" name="btn4" value="4" onClick="pressBtn(4)">
    <input type="button" name="btn3" value="3" onClick="pressBtn(3)">
    <input type="button" name="btn2" value="2" onClick="pressBtn(2)"><br>
    <input type="button" name="btn1" value="1" onClick="pressBtn(1)">
    <input type="button" name="btn0" value="0" onClick="pressBtn(0)">
    <input type="button" name="btnPlus" value="+" onClick="pressOP('+')">
    <input type="button" name="btnPlus" value="-" onClick="pressOP('-')"><br>
    <input type="button" name="btnPlus" value="x^y" onClick="pressOP('^')">
    <input type="button" name="btnPlus" value="*" onClick="pressOP('*')">
    <input type="button" name="btnPlus" value="/" onClick="pressOP('/')">
    <input type="button" name="btnPlus" value="." onClick="pressOP('.')"><br>
    <input type="button" name="btnPlus" value="C" onClick="pressOP('C')">
    <input type="button" name="btnEq" value="=" onClick="pressEq();">
  </form>
</div>