question

Danny,

That is the nature of how computers handle decimal precision values, particularly how C++ handles a division operation. There are lots of complicated explanations and papers about why it is done this way.

A relatively short explanation can be found on wikipedia: http://en.wikipedia.org/wiki/Floating_point

There is a section entitled "Accuracy problems" near the bottom of that article that explains it a bit.

Usually it doesn't matter that the precision is slightly off, but sometimes it messes with your logic when doing comparison operations as shown below.

The main issue is when you think it is going to get into one of the simple cases (==, <=, >=, <, >, or !) but it doesn't. There are a few things you can do to see if it is "close enough" though to avoid such precision comparison issues. I've included some of those in the following code as well. It happens that your example actually does work for the == test although ofttimes such division calculations wouldn't. You have to be careful in C++ with == when you are comparing to a double value that has been assigned based on a division or multiplication operation.

int test1 = 138.0;
int test2 = 50.0;
double test3 = test1/test2;

pt("dp number testx");pt(numtostring(test3, 54, 50));
pr();
if(test3 == 2.76)
{
 pt("exactly 2.76");
 pr();
}
if(fabs(test3 - 2.76) < 0.0001)
{
 pt("close enough to equal 2.76");
 pr();
}
if(test3 <= 2.76)
{
 pt("<= 2.76");
 pr();
}
if(test3-0.0001 <= 2.76)
{
 pt("close enough to <= 2.76");
 pr();
}
if(test3 >= 2.76)
{
 pt(">= 2.76");
 pr();
}
if(test3+0.0001 >= 2.76)
{
 pt("close enough to >= 2.76");
 pr();
}
return test3;

I hope this helps. Good luck.