Javascript program help

Question

Update this program is supposed to keep track of the number of times each side is rolled not each roll itself.

I am working on a javascript exercise that needs to take two dice, roll them 1000 times and keep track of each roll. I thought the best way to do it was to use an array but I am not exactly sure if I am going in the right direction with what I am doing. I just need a little help in pointing me in the right direction to get this to work because right now it doesnt output anything. Thanks here is my code:

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>Exercise Five</title>

<script type="text/javascript">
    function Die(){
        this.roll = function(){
            this.sides = 0;
            return parseInt((Math.random( ) * 1000) % this.sides) + 1;  
        }
    }
</script>

</head>

<body>
<script type="text/javascript">
    var dieOne = new Die();
    var dieTwo = new Die();
    var rollOne = 0;
    var rollTwo = 0;
    var roll_value = new Array();
    var arrayPlace = 0;

    for(var i = 0; i < 1000 ; i++){
        rollOne = dieOne.roll();
        dieOne.sides = 10;
        rollTwo = dieTwo.roll();
        dieTwo.sides = 10;
        arrayPlace = (rollOne + rollTwo) - 2;
        roll_value[arrayPlace]++;
    }

    for( var i = 0; i < roll_value.length; i++){
        document.writeln(roll_value[i]);
    }

</script>
</body>
</html>

dieOne.sides = 10; You probably want to do that before you roll the die, not after. And no need to reset this inside of the loop every time. — Thilo
– Thilo, Commented Sep 27, 2011 at 3:27
Sorry it doesnt output anything and i have checked it with the webdeveloper tools on firefox and it acts like everything is fine — shinjuo
– shinjuo, Commented Sep 27, 2011 at 3:27
var sides = 0; return parseInt((Math.random( ) * 1000) % sides) + 1; Looks like it would divide by zero every time. — Thilo
– Thilo, Commented Sep 27, 2011 at 3:28

Adam Eberlin · Accepted Answer · 2011-09-27 03:57:04Z

1

Sorry, see updated code below:

var dieOne = new Die();
var dieTwo = new Die();
var rollOne = 0;
var rollTwo = 0;
var roll_values = new Array();

for(var i = 0; i < 1000 ; i++){
  rollOne = dieOne.roll();
  rollTwo = dieTwo.roll();
  roll_values[i] = { 'first': rollOne,
                     'second': rollTwo,
                     'value': 0 };
  // 1. iterate through past roll_values[i].first, roll_values[i].second
  // in order to determine what you need to increment and by how much

  // 2. finally set roll_values[i].value = var_containing_value;
}

for( var i = 0; i < roll_value.length; i++){
  console.log(roll_value[i]);
}

And, another note, for debugging, console.log(whatever) is excellent and supported on most modern browsers (IE > 8, thanks Kolink). The console log will show up in the javascript/error console.

There were two problems: how you were storing the roll values and how you were incrementing your array. Both should now be fixed.

edited Sep 27, 2011 at 3:57

answered Sep 27, 2011 at 3:32

Adam Eberlin

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5 Comments

shinjuo Over a year ago

I have tested it again just to make sure but my random generation function works fine

shinjuo Over a year ago

I did have to change var sides back to this.sides, but it does work. That part was actually given to me in the book

shinjuo Over a year ago

Sorry I didnt specify enough, this program needs to keep track of each time the value is rolled. so if it rolls 2 5's then the roll amount is 10 and it needs to remember that 10 was rolled once. then when it rolls 10 again it needs to increment to 2 and so on and so fourth

Adam Eberlin Over a year ago

I've provided some hints which should help you. By using hash objects for your roll_values array, you can keep track of multiple values with ease, which should allow you all the history you need to determine appropriate values for the rolls.

Niet the Dark Absol Over a year ago

console.log() is supported in IE8+

RobG · Accepted Answer · 2011-09-27 04:09:49Z

1

Try this:

  function Dice(sides) {
    this.sides = sides;
  }

  Dice.prototype.roll = function() {
    return (Math.random() * (this.sides + 1)) | 0 ;
  }

  var counts = [];
  var d1 = new Dice(6);
  var d2 = new Dice(6);
  var s;

  for (var i=1000; i; i--) {
    s = d1.roll() + d2.roll();
    counts[s] = typeof counts[s] == 'undefined'? 1 : ++counts[s];
  }

  // Show results
  for (var i=0, iLen=counts.length; i<iLen; i++) {
    console.log(i + ' : ' + counts[i]);
  }

answered Sep 27, 2011 at 4:09

RobG

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