why math wont work?

**Fabian** · Jul 20 '05, 12:45 PM

Re: why math wont work?

Allen Thompson hu kiteb:
[color=blue]
> sorry for the simple question, haven't done this in a while. when I
> use the following script it keeps displaying the value of "x" like a
> string. for example, if I type the number 7 in the prompt, it
> displays the result as 721 instead of the answer I want which is 28.
> what am I doing wrong.
> hanks -Allen Thompson
>
> <html>
> <body>
> <script language="javas cript">
> var y=window.prompt ();
> var x=y+3*7;[/color]

var x = (y * 1) + (3*7);

Unless you force js to recognise a variable as a number, half teh time
it assumes it is text, and teh + operator is both addition and
concatenation.

If I had my way, + would be reserved as addition only, and a separate
operator created for concatenation.

--
--
Fabian
Visit my website often and for long periods!

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**Lasse Reichstein Nielsen** · Jul 20 '05, 12:46 PM

Re: why math wont work?

"Fabian" <lajzar@hotmail .com> writes:
[color=blue]
> var x = (y * 1) + (3*7);[/color]

Or
var x = Number(y)+3*7
or one of the other ways to convert a string into a number.

The important point is that y contains a string (prompt returns a
string), not a number, and that adding a number to a string will
always convert the number to a second string and concatenate the
strings.

<URL:http://jibbering.com/faq/#FAQ4_21>
[color=blue]
> Unless you force js to recognise a variable as a number, half teh time
> it assumes it is text, and teh + operator is both addition and
> concatenation.[/color]

It's not *that* bad. Javascript won't assume something half of the time.
It consistently treats strings as strings and numbers as numbers, and
when adding something to a string, it converts the other part to a string
and concatenates.

I would rather say that half of the time, you get away with forgetting
that you have a string containing a numeral, because Javascript converts
it to a number before doing arithmetic operations on it. E.g.,
var y = "42";
var x1 = y * 2; // 84
var x2 = y / 2; // 21
var x3 = y - 37; // 5
var x4 = y + 10; // 4210 - addition doesn't convert arguments to numbers.
In the first four cases, you can safely forget that y contains a string.
It's just that you can't always, so you shouldn't.
[color=blue]
> If I had my way, + would be reserved as addition only, and a separate
> operator created for concatenation.[/color]

I wouldn't complain about that. I guess the behavior is stolen from Java,
where + also does concatenation on strings.
/L
--
Lasse Reichstein Nielsen - lrn@hotpop.com
DHTML Death Colors: <URL:http://www.infimum.dk/HTML/rasterTriangleD OM.html>
'Faith without judgement merely degrades the spirit divine.'

**Douglas Crockford** · Jul 20 '05, 12:46 PM

Re: why math wont work?

> when I use the[color=blue]
> following script it keeps displaying the value of "x" like a string. for
> example, if I type the number 7 in the prompt, it displays the result as 721
> instead of the answer I want which is 28. what am I doing wrong.
> hanks -Allen Thompson
>
> <html>
> <body>
> <script>
> var y=window.prompt ();
> var x=y+3*7;
> document.write( x);
> </script>
> </body>
> </html>[/color]

prompt() returns a string. Before using the '+' operator, you need to convert
the string to a number.

var x = (+y) + 3 * 7;

JavaScript: A Survey of the Language

http://www.crockford.com/javascript/survey.html

**Dennis M. Marks** · Jul 20 '05, 12:46 PM

Re: why math wont work?

In article <bre3sh$2di3h$1 @ID-174912.news.uni-berlin.de>, Fabian
<lajzar@hotmail .com> wrote:
[color=blue]
> Allen Thompson hu kiteb:
>[color=green]
> > sorry for the simple question, haven't done this in a while. when I
> > use the following script it keeps displaying the value of "x" like a
> > string. for example, if I type the number 7 in the prompt, it
> > displays the result as 721 instead of the answer I want which is 28.
> > what am I doing wrong.
> > hanks -Allen Thompson
> >
> > <html>
> > <body>
> > <script language="javas cript">
> > var y=window.prompt ();
> > var x=y+3*7;[/color]
>
> var x = (y * 1) + (3*7);
>[/color]
<snip>

Just use var x=+y+3*7;

If the y was at the other end of the formula then
var x=3*7+(+y)

--
Dennis M. Marks

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**Dr John Stockton** · Jul 20 '05, 12:47 PM

Re: why math wont work?

JRS: In article <esvCb.43$im.42 @newsread2.news .atl.earthlink. net>, seen
in news:comp.lang. javascript, Allen Thompson <genericjoe@min dspring.com>
posted at Sat, 13 Dec 2003 03:12:10 :-[color=blue]
>sorry for the simple question, haven't done this in a while. when I use the
>following script it keeps displaying the value of "x" like a string. for
>example, if I type the number 7 in the prompt, it displays the result as 721
>instead of the answer I want which is 28. what am I doing wrong.[/color]

You basic error lies in omitting to read the newsgroup FAQ.

--
© John Stockton, Surrey, UK. ?@merlyn.demon. co.uk Turnpike v4.00 IE 4 ©
<URL:http://jibbering.com/faq/> Jim Ley's FAQ for news:comp.lang. javascript
<URL:http://www.merlyn.demo n.co.uk/js-index.htm> Jsc maths, dates, sources.
<URL:http://www.merlyn.demo n.co.uk/> TP/BP/Delphi/Jsc/&c, FAQ topics, links.

**Thomas 'PointedEars' Lahn** · Jul 20 '05, 12:48 PM

Re: why math wont work?

Dennis M. Marks wrote:
[color=blue]
> If the y was at the other end of the formula then
> var x=3*7+(+y)[/color]

JFTR:

var x = 3*7+ +y;

is also possible but more error-catching.

PointedEars

**Thomas 'PointedEars' Lahn** · Jul 20 '05, 12:48 PM

Re: why math wont work?

Douglas Crockford wrote:
[color=blue]
> prompt() returns a string.[/color]

It returns a string if the user confirms. Otherwise
it returns `null', no matter what has been typed.

PointedEars

**Lasse Reichstein Nielsen** · Jul 20 '05, 12:48 PM

Re: why math wont work?

Thomas 'PointedEars' Lahn <PointedEars@we b.de> writes:
[color=blue]
> Douglas Crockford wrote:
>[color=green]
>> prompt() returns a string.[/color]
>
> It returns a string if the user confirms. Otherwise
> it returns `null', no matter what has been typed.[/color]

That is browser dependent. Opera returns "undefined" , not "null".
Bot IE and Mozilla do return "null".

/L
--
Lasse Reichstein Nielsen - lrn@hotpop.com
DHTML Death Colors: <URL:http://www.infimum.dk/HTML/rasterTriangleD OM.html>
'Faith without judgement merely degrades the spirit divine.'

**Dauber!** · Jul 20 '05, 12:48 PM

Re: why math wont work?

Waaaaay back on 13-Dec-03 11:26:28, Douglas Crockford said this about Re: why math wont work?:
[color=blue][color=green]
>> following script it keeps displaying the value of "x" like a string. for
>> example, if I type the number 7 in the prompt, it displays the result as
>> 721 instead of the answer I want which is 28. what am I doing wrong. hanks
>> -Allen Thompson
>>
>> <html>
>> <body>
>> <script>
>> var y=window.prompt ();
>> var x=y+3*7;
>> document.write( x);[/color][/color]
[color=blue]
>prompt() returns a string. Before using the '+' operator, you need to convert
>the string to a number.[/color]
[color=blue]
> var x = (+y) + 3 * 7;[/color]

That'll still give the same result, unfortunately. Whatcha need to do is this;

var x = parseInt(y)+3*7 ;

That should work.

--
dauber@banana-and-louie.org * dauber.50megs.c om
* ICQ: 28677921 * YIM: dau_ber * AIM: ddaauubbeerr

**Thomas 'PointedEars' Lahn** · Jul 20 '05, 12:48 PM

Re: why math wont work?

Lasse Reichstein Nielsen wrote:
[color=blue]
> Thomas 'PointedEars' Lahn <PointedEars@we b.de> writes:[color=green]
>> Douglas Crockford wrote:[color=darkred]
>>> prompt() returns a string.[/color]
>>
>> It returns a string if the user confirms. Otherwise
>> it returns `null', no matter what has been typed.[/color]
>
> That is browser dependent. Opera returns "undefined" , not "null".[/color]

*Are* *you* *really* *really* *sure*? [psf 1.1]

My Opera/7.11 (Windows NT 5.0; U) [en] returns `null', too.

Done the following tests in the Location Bar:

javascript:aler t(prompt("bla") ) // `null' if canceled
javascript:aler t(typeof prompt("bla")) // `object' if canceled

PointedEars

**Thomas 'PointedEars' Lahn** · Jul 20 '05, 12:48 PM

Re: why math wont work?

Dauber! wrote:[color=blue]
> Waaaaay back on 13-Dec-03 11:26:28, Douglas Crockford said this about Re: why math wont work?:[/color]

The recommended, if not even standardized, maximum is 78 characters
per line. Besides, about 74.7% of your attribution is composed of
superfluous information.
[color=blue][color=green]
>>prompt() returns a string. Before using the '+' operator, you need to convert
>>the string to a number.[/color]
>[color=green]
>> var x = (+y) + 3 * 7;[/color]
>
> That'll still give the same result, unfortunately.[/color]

Not in my UAs. But I think you do not
want to be taken seriously, so go away.
[color=blue]
> Whatcha need to do is this;
>
> var x = parseInt(y)+3*7 ;
>
> That should work.[/color]

See the FAQ about parseInt(...).

And of course it will work, but the above
is about 6 times faster and more reliable.
[color=blue]
> --[/color]

The trailing space is missing.

PointedEars

**HikksNotAtHome** · Jul 20 '05, 12:48 PM

Re: why math wont work?

In article <807.478T2962T1 0846128dau_ber@ verizon.SPAMISF OREATING.net.in valid>,
"Dauber!" <dau_ber@verizo n.SPAMISFOREATI NG.net.invalid> writes:
[color=blue][color=green]
>> var x = (+y) + 3 * 7;[/color]
>
>That'll still give the same result, unfortunately. Whatcha need to do is
>this;[/color]

Did you bother testing that before spouting off that it would give the same
results?
It is *well* known in this group that +y where y is a number in a string format
is quicker at converting it to a number than parseInt is, which you use
incorrectly.

[color=blue]
>var x = parseInt(y)+3*7 ;
>
>That should work.[/color]

As long as y doesn't start with a 0 or 0x format.

http://www.jibbering.com/faq/#FAQ4_12

--
Randy

**Lasse Reichstein Nielsen** · Jul 20 '05, 12:48 PM

Re: why math wont work?

Thomas 'PointedEars' Lahn <PointedEars@we b.de> writes:
[color=blue]
> *Are* *you* *really* *really* *sure*? [psf 1.1][/color]

*Yes* *I* *am*!
[color=blue]
> My Opera/7.11 (Windows NT 5.0; U) [en] returns `null', too.[/color]

My Opera/7.23 (Windows NT 5.1; U) [en] returns 'undefined'
[color=blue]
> javascript:aler t(typeof prompt("bla")) // `object' if canceled[/color]

on this exact test.

/L
--
Lasse Reichstein Nielsen - lrn@hotpop.com
DHTML Death Colors: <URL:http://www.infimum.dk/HTML/rasterTriangleD OM.html>
'Faith without judgement merely degrades the spirit divine.'

**Dauber!** · Jul 20 '05, 12:48 PM

Re: why math wont work?

Waaaaay back on 14-Dec-03 19:16:53, HikksNotAtHome said this about Re: why math wont work?:
[color=blue][color=green][color=darkred]
>>> var x = (+y) + 3 * 7;[/color]
>>
>>That'll still give the same result, unfortunately. Whatcha need to do is
>>this;[/color][/color]
[color=blue]
>Did you bother testing that before spouting off that it would give the same
>results?[/color]

Uhhh....yes. Believe it or not, despite popular belief, not all browsers
interpret JavaScript the same way, including two of the ones I use.
[color=blue]
>It is *well* known in this group that +y where y is a number in a string
>format is quicker at converting it to a number than parseInt is, which you
>use incorrectly.[/color]

Funny...two references I checked, including one that helped me get an A in
my JavaScript programming class that I took for my webmaster admin
certification, indicates that it's perfectly valid; in fact, I'm given
several overloaded versions tht account for "0x" format as well as binary
and octal...

--
dauber@banana-and-louie.org
* ICQ: 28677921 * YIM: dau_ber * AIM: ddaauubbeerr

why math wont work?

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