Is it wrong to compare a double to 0 like this: doubleVariable==0?

It is ok to do this?

double doubleVariable开发者_运维问答=0.0;
if (doubleVariable==0) {
   ...
}

Or this code would suffer from potential rounding problems?

Nope it's perfectly legal if you are only going to compare against 0 as the right side of comparison will automatically casted to double. On the other hand, it would yield all the round-off errors if you where to compare against == 0.10000001

You are better or reading the discussion about float to 0 comparison here: Is it safe to check floating point values for equality to 0?

Also this discussion is very informative about weird precision problems on floats: Why the result is different for this problem?

i.e. below will yield false:

double d1 = 1.000001; double d2 =0.000001;
Console.WriteLine((d1-d2)==1.0);

What you have there is 0, which is an integer literal. It is implicitly converted to a double which you could represent with the double literal 0.0 (implicit conversion). Then there is a comparison between the two doubles. A rounding error could cause doubleVariable to not be equal to 0.0 (by some other math you might do, not just setting it), but there could never be a rounding error when converting the integer 0 to double. The code you have there is totally safe, but I would favor == 0.0 instead.

Try:

if (double.Equals(doubleValue, 0.0)){}

If you're just comparing a double variable against 0.0 (or 0), I believe it's safe to do it that way because I think 0 can be represented exactly in floating point, but I'm not 100% sure.

In general, the suggested approach for comparing floating point numbers is to choose a "delta" value at which you'll consider two doubles to be equal if their difference is less than the delta. This handles exact representation limitations with floating point numbers.

double first = 1.234;
double second = 1.2345;
double difference = Math.Abs(first - second);

double threshold = 0.000001; // doubles are equal if their difference is less than this value - you choose this value based on your needs
bool areEqual = difference < threshold;

hmm... I think as long as the number has an exact binary fraction representation (like 0) the comparison is perfectly valid.

You should not use double for such comparision. double creates problem.
e.g double n1=0.55 double n2=100 then double ans=n1*n2 should be 55.0
but when you debug ans is 55.000000000000007. if(ans==55.0)
will fail. in such case you can face a problem.