Estimating Pi in Javascript

Question

I’m trying to estimate Pi, but I get one NaN.

var x = 0
var y = 0
var fora = 0
var dentro = 0
var f = document.querySelector('input#t')
var t = Number(f.value)
var pi = document.querySelector('div#pi')
var atual = 0
var distance = 0

function start() {
  while (atual < t) {
    x = Math.random()
    y = Math.random()
    distance = x ** 2 + y ** 2
    if (distance <= 1) {
      dentro += 1
      atual += 1
    } else {
      fora += 1
      atual += 1

    }
  }
  pi.innerHTML = 4 * dentro / fora
}

<h1>Calculador de pi</h1>
<p>Insira um número de tentavicas</p><input type="number" name="t" id="t"><input type="button" value="start" onclick="start()">
<div id="pi">asdas</div>

Answer 1

Some errors present in your code:

• start the variable t out of function start. In this case, the variable will be executed when the HTML is created, and in this step, the value of the text box is empty, causing f.value be it '' and Number('') be it NaN.

• dividing dentro for fora instead of atual.

You can fix them that way:

var f = document.querySelector('input#t')
var pi = document.querySelector('div#pi')

function start() {
  var x = 0
  var y = 0
  var fora = 0
  var dentro = 0
  var atual = 0
  var distance = 0
  var t = parseInt(f.value)

  while (atual < t) {
    x = Math.random()
    y = Math.random()
    distance = x ** 2 + y ** 2
    if (distance <= 1) {
      dentro += 1
      atual += 1
    } else {
      fora += 1
      atual += 1
    }
  }
  pi.innerHTML = 4 * dentro / atual
}

<h1>Calculador de pi</h1>
<p>Insira um número de tentavicas</p><input type="number" name="t" id="t"><input type="button" value="start" onclick="start()">
<div id="pi">asdas</div>