Simple Compiler Question

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I was working with Visual Studio 2005 on a relatively simply problem, but it was fairly heavy in mathematical calculations. However, my program simply was not giving me the correct output and I could not figure out why. Long story short, I found out it was because I was basically doing this:

double x = 2/5;

However, I eventually found out that the compiler was turning that into 0 instead of .4! If I entered...

double x = .4;

Then it worked correctly. Is this an issue that was fixed in more recent Visual Studios, or what? I was extremely disappointed (yet also relieved since the program was so simple yet I was unable to do it!) when I figured out that it was as simple as a "fraction" being set to 0 instead of being divided out.

Posted 3-May-10 16:40pm

slapshot6819

Updated 3-May-10 20:19pm

Moak

v2

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Christian Graus · Accepted Answer · 2010-05-03T17:07:00

Solution 1

This is an issue with the C++ standard. The compiler is doing EXACTLY what you ask of it.

2/5

is the same as

(int)2/(int)5

So, the result that is returned, is an int, which is THEN turned into a double.

2/(double)5 or
2/5.0

will work fine.

Posted 3-May-10 17:07pm

Christian Graus

Comments

slapshot6819 4-May-10 1:12am

Thanks for the response, very informative. Interesting. Interesting, but annoying. I rewrote my code and redid the math multiple times before I finally found out the problem heh...

Emilio Garavaglia 7-May-10 7:50am

Welcome to the C++ enigmistics!