World of Tanks Crew Training Calculator

 <!DOCTYPE html>
<html>
<head>
<title>Training Book Calculator</title>
</head>
<body>

<script>
function CalcIncrease( pcent, skills, xp, nb ) {

    var keep_trying = 1, y, xp_req;

    xp = xp * nb;

    while ( keep_trying == 1 ) {
        y = skills + 2;
        xp_req = ( 2 ** y ) * 25 * ( 100 ** ( pcent / 100 ) );

        if ( xp_req <= xp ) {
            xp = xp - xp_req;
            pcent++;

            if ( pcent == 100 ) {
                skills++;
                pcent = 0;
            }
        } else {
            keep_trying = 0;
        }
    }

    document.getElementById("noskills").innerHTML = "After applying the book(s), you will have " + skills + " completed skills and be at " + pcent + " percent in the next.";
    return " ";
}
</script>

<h1>Calculate the crew skill resulting from the application of crew books</h1>

<form onsubmit="return false" onchange="x.value=CalcIncrease(parseInt(a.value), parseInt(noperks.value), parseInt(books.value), parseInt(nb.value))">

 <input type="radio" name="noperks" value="0" checked> No completed skills<br>
  <input type="radio" name="noperks" value="1"> One completed skill<br>
  <input type="radio" name="noperks" value="2"> Two completed skills<br>
  <input type="radio" name="noperks" value="3"> Three completed skills<br>
  <input type="radio" name="noperks" value="4"> Four completed skills<br>
  <input type="radio" name="noperks" value="5"> Five completed skills<br>
  <input type="radio" name="noperks" value="6"> Six completed skills<br><br><br>
  Percent in current skill (0-99)
  <input type="number" id="a" step="1" name="a" min="0" max="99" value="50" >
  <br>
  <input type="number" id="nb" step="1" name="nb" min="1" max="50" value="1" >
   <select name="books">
  <option value="20000">20,000 XP book</option>
  <option value="100000">100,000 XP book</option>
  <option value="250000">250,000 XP book</option>
  <option value="850000">850,000 XP book</option>
</select>
  <output name="x"></output>
</form>
<p id="noskills" ></p>

</body>
</html>