Java script addition of numbers with giving wrong answer

Question

I am working with a simple java script code which goes here

<script>
var x=prompt("Enter a number");
var n=x+2;
alert(n);
</scrip>

This code will throws a prompt If i enter 2 in the prompt.I am expecting output as 4,But it is generating 22 in alert. What mistake is happening here.

Because user enter a string and your number will be converted to string. Try enter "18" and you'll see "182". Check parseInt() on MDN. — Adriano Repetti
– Adriano Repetti, Commented Oct 26, 2014 at 17:56

Andre Pena · Accepted Answer · 2014-10-26 17:55:20Z

4

Yes.

 var n;
 if(!isNaN(x)) {
    n = parseInt(x) + 2; // make sure x is always a number here
 }

This is because the prompt function will return an String, not a number.

String + Number = String

answered Oct 26, 2014 at 17:55

Andre Pena

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Comments

sbrbot · Accepted Answer · 2014-10-26 17:55:35Z

0

<script>
var x=prompt("Enter a number");
var n=parseInt(x)+2;
alert(n);
</scrip>

answered Oct 26, 2014 at 17:55

sbrbot

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2 Comments

Wouter J Over a year ago

Instead of showing a correct answer, you could better describe what was going wrong in the code used by the person who asked the question.

Matt Over a year ago

All you would need to do to make this better is give a nod to the comment from @adrianorepetti

Patricia · Accepted Answer · 2014-10-26 17:58:09Z

0

Try

<script>
var x = prompt("Enter a number");
var n = parseInt(x)+2;
alert(n);
</script>

answered Oct 26, 2014 at 17:58

Patricia

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Comments

friedi · Accepted Answer · 2014-10-26 18:04:43Z

0

Here an alternative way of doing this:

var x = +prompt("Enter a number");
var n = x+2;
alert(n);

The plus sign (in front of prompt) converts the string to a number.

answered Oct 26, 2014 at 18:04

friedi

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