Having problems with my JavaScript Equation (Part of Binary to Decimal Converter)

Question

So this is an outrage, a simple equation results in a random number that I can make little sense of.

Ok, so I am trying to make an app that converts from Binary to Base Ten. I know one way of doing this is to do this.

Say, 11001 to base ten.

Take the left-most digit: 1

0 * 2 + 1(This 1 is the leftmost binary digit) = 1...
1 * 2 + 1(This 1 is the second leftmost binary digit) = 3...
3 * 2 + 0(etc...) = 6...
6 * 2 + 0 = 12...
12 * 2 + 1 = 25...

So, that correctly converts into 25. Although, when I plug that equation with variables in JavaScript, it turns out random crap.

Watch:

Inputarray is an array of all the characters in the number the user inputted. So, if 11010, then inputarray is 1,1,0,1,0.

Then it loops over each character of the array and plugs each number into the equation as shown.

for (var j=0;j<=uinputlen;j++) {
var nextletter = uinput.charAt(j);
inputarray.push(nextletter);
}

for (var h=0;h<=uinputlen;h++) {
decvalue = decvalue * 2 + inputarray[h];
}

BTW, "decvalue" is preset to 0 at the beginning of my code.

Please comment on any questions on the description or anything else, it is kind of confusing.

Looking at the answers given so far, it seems nobody has ever heard of `parseInt`, `toString`... or even bit-shift operators. — Niet the Dark Absol, Jan 02 '13 at 21:36

score 3 · Answer 1 · answered Jan 02 '13 at 21:26

3

JavaScript can do this natively:

var binary = "11001";
var decimal = parseInt(binary,2);

// other way:

var decimal = 1234;
var binary = decimal.toString(2);

answered Jan 02 '13 at 21:26

Niet the Dark Absol

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So does this turn it into base ten or just turns it into a string? – austinstout Jan 02 '13 at 21:32
The first one turns binary into decimal using `parseInt`. The second one turns a decimal number into binary using `toString`. In both cases the `2` tells JavaScript you want binary. You can use similar code to convert to pretty much any base. – Niet the Dark Absol Jan 02 '13 at 21:35
ARE YOU KIDDING ME I SPENT HOURS ON THIS AND I COULD HAVE DONE JUST THAT!!!!!! AUGH! – austinstout Jan 02 '13 at 21:59
Eeeeyup. I've made the same mistake ;) – Niet the Dark Absol Jan 02 '13 at 21:59

Krizz · Answer 2 · 2013-01-02T21:33:42.623

0

You are adding a character code, not the value digit represents. .charAt() will return '0' or '1' which is a string and, therefore, it will be added as a string.

I suggest you change how you push values to the following:

inputarray.push(nextletter == '1' ? 1 : 0)

or

inputarray.push(nextletter * 1)

edited Jan 02 '13 at 21:33

answered Jan 02 '13 at 21:26

Krizz

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charAt returns the string at that position, and adding a number to a string concatenates, it doesn't convert to the char code. – Jim Deville Jan 02 '13 at 21:28

score 0 · Answer 3 · answered Jan 02 '13 at 21:27

Since you are getting characters in your input array, JavaScript is converting the result to strings:

var a = 0; a = a * 2 + '1'; alert(a); //alerts "01"

In order to get your desired behavior, you need to cast the string:

var a = 0; a = a * 2 + Number('1'); alert(a); //alerts 1

In general, there are better ways to do this though, (such as @Kolink's answer)

See http://www.quirksmode.org/js/strings.html#stringnum for more information.

Having problems with my JavaScript Equation (Part of Binary to Decimal Converter)

3 Answers3