Adding two doubles gives incorrect result?

[Guest]

Hi

Looking at the following code ...

double a = 100.1;
double b = 0.1;
double c = a + b;

I would like to know why the value of c is 100.19999999999999 and not 100.2?

What should I do to correct this.

Thanks.

 

[Fred Mellender]

Floating point types (Float, Double) cannot hold exactly certain decimal
numbers. You could use the Decimal type if you need exact decimal
arithmetic, or use a subroutine package (e.g. GMP Bignum Library) if your
needed precision is greater than what Decimal can provide.

Or, you could do your arithmetic in floating point, convert the answer to
Decimal, and then round that to the precision you need.

 

[vladislav zalesak]

It has to do with the way a PC stores floating point types. if one value
compared to the other is too much smaller, the computer "discards" part
of the smaller number leading to "errors" like this.

 

[Jon Skeet [C# MVP]]

Looking at the following code ...

double a = 100.1;
double b = 0.1;
double c = a + b;

I would like to know why the value of c is 100.19999999999999 and not 100.2?

See http://pobox.com/~skeet/csharp/floatingpoint.html

What should I do to correct this.

Well, you're not going to get infinite precision with any of the built-
in types, but for arithmetic like the above, the decimal type would
help you.