Issue with Convert.ToDouble

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I used the below code for a math operation

Convert.ToDouble("80.1") * 100000.0

The answer i was supposed to get is 8010000 (Check in calculator). But the asnwer the above line gave me was 8009999.9999999991. Can anyone please tell me why this is happening and what is the correct way to do this math operation?

Posted 28-Jun-15 18:13pm

Member 11745595

Updated 28-Jun-15 18:14pm

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sasanka sekhar panda 29-Jun-15 0:27am

Please share some more details as this code work fine for me..

CPallini 2-Jul-15 3:52am

(Check in calculator)
Fantastic!

3 solutions

Solution 4

you can use math.Round method for getting the expected output

Posted 1-Jul-15 21:44pm

Lucifier Rocks

Solution 3

Thanks for the reply guys. Like mentioned in the link my computer might be having issues representing floating point correctly.

Using Convert.ToDecimal("80.1") * Parse.Decimal("100000.0") gives me the exact result.

Posted 29-Jun-15 8:02am

Member 11745595

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User 59241 · Accepted Answer · 2015-06-28T18:29:00

There is no issue. This is expected as your computer cannot exactly represent all floating point numbers. See here:
http://effbot.org/pyfaq/why-are-floating-point-calculations-so-inaccurate.htm[^]

and here:
http://stackoverflow.com/questions/2100490/floating-point-inaccuracy-examples[^]

and if you wish to go further here:
http://docs.oracle.com/cd/E19957-01/806-3568/ncg_goldberg.html[^]

There are many other links you can find on this subject including this:
Five Tips for Floating Point Programming[^]

If you poke a little deeper you will find 100000.0 can be represented exactly but 80.1 cannot being 80.099999999999994. The exact result of the multiplication may also not be able to be represented exactly so we get to your situation.

You may also wish to look at the decimal type which has greater precision over a smaller range. This particularly applies to money values.
https://msdn.microsoft.com/en-us/library/364x0z75.aspx[^]