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POJavascript arrays giving NaN
 

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  1. POJavascript arrays giving NaN
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    <p>I have a bit of HTML that is supposed to bounce ball(s) around the canvas, but the arrays storing the coordinates seem to be 'NaN' when I set them to a random position and test with <code>alert("Co-ordinates " + (cirX[i]) + " x " + (cirY[i]));</code>. This returns 'Co-ordinates NaN x NaN'. I have tried to do it with one ball without the arrays and it worked. I am not sure if I am coding my arrays badly or if it is something else. Here is my HTML:</p> <pre><code>&lt;!Doctype HTML&gt; &lt;head&gt; &lt;script&gt; var cirX = []; var cirY = []; var chX = []; var chY = []; var width; var height; function initCircle(nBalls) { alert(nBalls) for(var i = 0; i&lt;nBalls;i++) { alert("loop " + i) chX[i] = (Math.floor(Math.random()*200)/10); chY[i] = (Math.floor(Math.random()*200)/10); cirX[i] = Math.floor(Math.random()*width); cirY[i] = Math.floor(Math.random()*height); alert("Co-ordinates " + (cirX[i]) + " x " + (cirY[i])); circle(cirX[i],cirY[i],3); setInterval('moveBall(i)',10); } } function moveBall(ballNum) { if(cirX[ballNum] &gt; width||cirX[ballNum] &lt; 0) { chX[ballNum] = 0-chX[ballNum]; } if(cirY[ballNum] &gt; height|| cirY[ballNum] &lt; 0) { chY[ballNum] = 0-chY[ballNum]; } cirX[ballNum] = cirX[ballNum] + chX[ballNum]; cirY[ballNum] = cirY[ballNum] + chY[ballNum]; circle(cirX[ballNum],cirY[ballNum],3); } function circle(x,y,r) { var c=document.getElementById("canvas"); var ctx=c.getContext("2d"); canvas.width = canvas.width; ctx.fillStyle="#FF0000"; ctx.beginPath(); ctx.arc(x, y, r, 0, Math.PI*2, true); ctx.fill(); width = canvas.width; height = canvas.height; } &lt;/script&gt; &lt;/head&gt; &lt;body&gt; &lt;canvas id="canvas" width="400" height="300"&gt; &lt;/canvas&gt; &lt;script&gt; initCircle(3); //this sets the number of circles &lt;/script&gt; &lt;/body&gt; </code></pre> <p>I have looked up how to initialise arrays e.c.t, but I seem to be doing it right? Thanks in advance for your help!</p> <p><strong>EDIT:</strong><br> Despite fixing the above problems, only one ball moves and at varying speeds despite the variable <code>ballNum</code> in <code>moveBall()</code> varying from 0 to 2 as expected (tested by adding <code>alert(ballNum)</code>). Does anyone know why?</p>
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    1. USDaniel Causebrook
    1. USDaniel Causebrook
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      1. VTUpMod
    1. COI think the index is messed up, did you check the value of i, before retrieving cirX[i]?
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      1. USStormherz
    2. CONo, I think the index is fine. My problem was that width was not defined. Also, `alert("loop " + i)` checks i. @Stormherz
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      1. POJavascript arrays giving NaN
      1. USDaniel Causebrook
 

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