1. Registered User
Join Date
Oct 2009
Posts
4

## [RESOLVED] Some for loop help please.

Hi folks. Here's the code I have so far:

Code:
```<script language=javascript type=text/javascript>
var i, sum=0;

for (i=1;i<=5;i++)
{
sum = sum+i;
document.write("The total is: " +sum);
document.write("<br>");
}
</script>```
What I now need to do is modify the above to allow the user to input a value. So basically that would be 1+2+3+4+5+n?

I made an attempt at it, but I just don't know where to put n in the loop. I am very new to javascript.

Attempt:
Code:
```<html>
<title>For Loop</title>
<script language=javascript type=text/javascript>
var i, sum=0;
var n =eval(document.myform.number.value);

for (i=1;i<=5;i++)
{
sum = sum+i;
document.write("The total is: " +sum);
document.write("<br>");
}
</script>

<body>
<form name="myform" onSubmit="calculate();">
<h2>Enter a number</h2>
<p><label for="number">Input number here: </label><input type="text" size="10" name="number" id="number"/> </p>
<input type="submit" value="Calculate"/>
</form>

</body>
</html>```
Anyway thanks.

2. First things first, I would definitely NOT use that eval() statement to get the number out since there is unvalidated user input and they could put anything (e.g. "alert(\"hello\");" or something annoying).

What you should probably do is create a function which does your calculation for you and then writes it to a specific element. So, exemplia gratia:

Code:
```//Define the function
function doMySum() {
//First get the number from the user input
//I assume this should be an integer, rather than a float?
var n = document.getElementById("number").value.parseInt();

//Create an empty string to hold your "The total is: ..." stuff
var sum_string = "";

//Create iterator and sum variables
var i;
var sum = 0;

//Now run the for loop
for(i=0; i < n; i++) {
sum = sum + (i+1);

//Add a <br/> before this line if it's not the first line
if(i>0) { sum_string += "<br/>"; }

//Write the sum string
sum_string += "The total is: " + sum;
}

//Now write the output to a div called "output".
//This will over-write anything currently in there.
document.getElementById("output").innerHTML = sum_string;

//Return false to stop any links being followed or forms being submitted.
return false;
}```
HTML Code:
`onsubmit="return doMySum();"`
to the form tag.
Don't forget to create the "output" element (a <div>) should do the trick.

I hope that helps.
Last edited by blue-eye-labs; 10-27-2009 at 08:19 PM. Reason: HTML entities were messed around with.

3. Sorry, that should be
Code:
`var n = parseInt(document.getElementById("number").value);`
Code:
`var n =document.getElementById("number").value. parseInt();`
Apologies.

4. Originally Posted by blue-eye-labs
Sorry, that should be
Code:
`var n = parseInt(document.getElementById("number").value);`
Better
Code:
`var n = parseInt(document.getElementById("number").value, 10);`
If no base radix specified, parseInt() might consider some decimal numbers as octal, because, in fact, parseInt(number,base) method was designed to parse a number from a certain base to decimal. It is safer to specify which is that certain base, 10 in your case.

See:
Code:
```var x='0112';
Last edited by Kor; 10-28-2009 at 08:08 AM.

5. @Kor:

Thanks for that, I hadn't realised.

6. Registered User
Join Date
Oct 2009
Posts
4
Thank-you both for your replies that works perfectly

I assume that if I want to limit the number input by the user I would use an if statement and have a message show telling them to input a number between 0 and 20?

7. I assume that if I want to limit the number input by the user I would use an if statement and have a message show telling them to input a number between 0 and 20?
Yup, just check the value of n and if it's outside of your range then have some sort of popup, alert, red-div or whatever else you can think of

8. Registered User
Join Date
Oct 2009
Posts
4
Ok, thanks for the help dude

9. You're welcome. Mark the thread as resolved.

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