Double valules comparison using C/C++

[agurrea]

Please help...I am having a problem with comparing double values in C++. I have stumble across this issue when my sorting algorithm tries to compare double values to check whether a < b / a > b. Based on the comparison result my sorting algorithm does sorting by ascending or sorting in descending order.

However when I have something like the following double value comparison it yields different behavior.

Example:

double dValue1 = 10.5
double dValue2 = 10.10;

If i'm going to compare using > operator in C++ turns out the result is different than what I am expecting.

10.5 is compared to 10.1 --> looks to me there's a rounding issue here since it doesn't account for the floating point precision.

Hope there's someone who could share his/her idea on how to fix this bug.

I mean ultimately, I would expect that 10.10 should be greater than 10.5 when we compare both double values.

Thanks,
alein

[thomas_naveen]

Why should 10.1 be greater than 10.5?

Can you add your code to the post so that there is more clarity?

[Salem]

> I mean ultimately, I would expect that 10.10 should be greater than 10.5 when we compare both double values.
Huh?

So if I wrote the same values as
10.10 and 10.50
would that change anything for you?

Because it doesn't change anything for the compiler, or the numbers.

[agurrea]

Hello,

No, it doesn't change actually when comparing two double values 10.5 and 10.10 actually yields the same comparison result as 10.50 and 10.10.

I supposed the problem was that in my program the 10.5 which is actually a version number previously stored as a string before conversion to double was already having that notation. I thought it should be 10.05 because the 10.5 in double lexically means 10.50 isn't it?

thanks,
alein

[WaltP]

No, what the problem is your understanding of numbers.

10.1 is identical to 10.10 is identical to 10.1000000
Each is 10 and 1 tenth. It doesn't matter how many zeros you add.

Therefore, 10.5 (10 and 5 tenths) > 10.10000000

[agurrea]

Thank you all for your feedback now I understand the semantics of numbers represented as double values.

Cheers,
alein