weird math calculation

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Is JavaScript's Math broken?

I have a javascript and html code here my code

and i get a weird value when calculate specific fields. Only one checkbox has a script right now (the background music addon) and only when i select that add on with 1 of any of the 3in reels i get 24.990000000000002 in the total price. it's so weird its only with those inputs...it should be just 24.99....all the other inputs work and give accurate totals but just the 3 3in fields give those numbers...through trial and error I have found that the problem lies here

regthreetot = parseFloat(regthree * 50);
regfourtot = parseFloat(regfour * 100);
regfivetot = parseFloat(regfive * 200);
regsixtot = parseFloat(regsix * 300);
regseventot = parseFloat(regseven * 400);
supthreetot = parseFloat(supthree * 50);
supfourtot = parseFloat(supfour * 100);
supfivetot = parseFloat(supfive * 200);
supsixtot = parseFloat(supsix * 300);
supseventot = parseFloat(supseven * 400);
sixthreetot = parseFloat(sixthree * 50);
sixfourtot = parseFloat(sixfour * 100);
sixfivetot = parseFloat(sixfive * 200);
sixsixtot = parseFloat(sixsix * 300);
sixseventot = parseFloat(sixseven * 400);

the regthree,supthree and sixthree values are all multiplied by 50...all the other values are multiplied by a value with 3 digits...if i change 50 to 100 it will give a normal answer...why does the number of digits matter here and what can i do to fix it?

[Don't use floats for money](http://stackoverflow.com/questions/3730019/why-not-use-double-or-float-to-represent-currency) — Mat, Aug 02 '12 at 05:54
Also http://stackoverflow.com/questions/661562/how-to-format-a-float-in-javascript — John Carter, Aug 02 '12 at 05:55
interesting im reading this stuff now....is there something else i can use in the same place or do i have to code it differently... — user1556319, Aug 02 '12 at 05:58
The idea is to keep track of cents as wholes in a separate variable, and concatenate the final output at last. — elclanrs, Aug 02 '12 at 05:59
alright cool....no sure how to do that but ill figure it out...the method below is working for now though :) NOW I CAN SLEEP lol — user1556319, Aug 02 '12 at 06:03

score 0 · Answer 1 · answered Aug 02 '12 at 05:55

0

It happens because of the way float arithmetic works. You can work around it by rounding to 2 decimal places (you won't be using fractions of a cent anyways): http://jsfiddle.net/vSsW9/1/

answered Aug 02 '12 at 05:55

wow this is amazing and works thank you so much...its nice to have different ways to do things! – user1556319 Aug 02 '12 at 05:59
ohh if you see this again i have another question with the check box...so basically the value stays if i don't uncheck the box (if i press the clear button the function for the checkboxes doesn't get activated)...is there a function to clear a certain variable i can put in the clear buttons onclick? – user1556319 Aug 02 '12 at 06:08

score 0 · Answer 2 · answered Aug 02 '12 at 05:56

0

Well until you get it figured out you can use Math.Round to round to two decimals. Assume your resulting var is called result, do result=Math.round(result*100)/100

answered Aug 02 '12 at 05:56

Branden S. Smith

1,161
7
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i actually used math.round in my code already...just not for that part.. but the guy above put .toFixed(2) beside the total...is that tje same thing? – user1556319 Aug 02 '12 at 06:01
ohh if you see this again i have another question with the check box...so basically the value stays if i don't uncheck the box (if i press the clear button the function for the checkboxes doesn't get activated)...is there a function to clear a certain variable i can put in the clear buttons onclick? – user1556319 Aug 02 '12 at 06:08

score 0 · Answer 3 · answered Aug 02 '12 at 07:05

0

It's caused by float variables not being 100% accurate, to fix it to max 2 decimal points:

n.toFixed(2)

answered Aug 02 '12 at 07:05

Luka

341
2
11

weird math calculation

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