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I don't understand why the below JavaScript program returns the answer Infinity. What am I doing wrong? I'm a novice, and would appreciate a detailed explanation!

Please note that this needs to be acplished using only math and math functions, no string functions or arrays!

<script type = "text/javascript">

var input;
var rev = 0;

input=window.prompt ("Please enter a 5-digit number to be reversed.");

input = input * 1;

while (input > 0)
{
   rev *= 10;
   rev += input % 10;
   input /= 10;
}
document.write ("Reversed number: " + rev);

</script>

I don't understand why the below JavaScript program returns the answer Infinity. What am I doing wrong? I'm a novice, and would appreciate a detailed explanation!

Please note that this needs to be acplished using only math and math functions, no string functions or arrays!

<script type = "text/javascript">

var input;
var rev = 0;

input=window.prompt ("Please enter a 5-digit number to be reversed.");

input = input * 1;

while (input > 0)
{
   rev *= 10;
   rev += input % 10;
   input /= 10;
}
document.write ("Reversed number: " + rev);

</script>
  • algorithm
  • javascript
Share Improve this question asked Aug 8, 2011 at 23:50 sls3nycsls3nyc 5
  • 2 You seem to have an answer already, so there's probably no point posting elsewhere, but for future reference: this site is for puzzles in the sense of games. For puzzles in the sense of bugs you don't understand, the main StackOverflow site is the appropriate one. – Peter Taylor Commented Aug 9, 2011 at 6:38
  • It can (and should) still be migrated to its proper place. – Joey Commented Aug 9, 2011 at 8:41
  • @Joey, except that the proper place isn't an option in the migration targets. The only option is meta.codegolf, for some reason. – Peter Taylor Commented Aug 9, 2011 at 8:44
  • 1 Leave that to the mods. They can do things we can never ask for. – Joey Commented Aug 9, 2011 at 8:45
  • I've started a thread on meta – Peter Taylor Commented Aug 9, 2011 at 8:46
Add a ment  | 

2 Answers 2

Reset to default 4

Your line: input /= 10; doesn't result in an integer. You end up with a sequence like this:

input  rev
1234.5 5
123.45 54.5
12.345 548.45

This never hits 0, so your while condition just keeps going till it reaches 1e-323, then the number runs out of precision and goes to 0.

If you replace the input /= 10; line with input = Math.floor(input/10); then it works.

Because this is code golf you probably don't want to use Math.floor though. There is a smaller one, I'll see if I can find it again.

You can use input = ~~(input/10); provided input is always positive.

<html>
<head>
<script type="text/javascript">
function reversing(x){
  y=x%10;
  x=parseInt(x/10);
    document.write(y);
     if(x!=0){
      reversing(x);
     }
}
</script>
</head>

<body>
<input id="txt_field" type="text" name="field" />
<input type="button" name="submit" value="Submit" onclick="reversing(document.getElementById('txt_field').value);"/>
</body>
</html>

本文标签： algorithmJavascript program to print a number series in reverseStack Overflow

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