Question

Possible Duplicate:
problem in comparing double values in C#

I’ve read it elsewhere, but really forget the answer so I ask here again. This loop seems never end regardless you code it in any language (I test it in C#, C++, Java…):

double d = 2.0;
while(d != 0.0){
   d = d - 0.2;
}

Answer 1

Floating point calculations are not perfectly precise. You will get a representation error because 0.2 doesn’t have an exact representation as a binary floating point number so the value doesn’t become exactly equal to zero. Try adding a debug statement to see the problem:

double d = 2.0;
while (d != 0.0)
{
    Console.WriteLine(d);
    d = d - 0.2;
}

2
1,8
1,6
1,4
1,2
1
0,8
0,6
0,4
0,2
2,77555756156289E-16   // Not exactly zero!!
-0,2
-0,4

One way to solve it is to use the type decimal.