Why float.NaN != double.NaN in C#?

Question

Why float.NaN != double.NaN ?

while float.PositiveInfinity == double.PositiveInfinity and float.NegativeInfinity == double.NegativeInfinity are equal.

EXAMPLE:

bool PosInfinity = (float.PositiveInfinity == double.PositiveInfinity); //true bool NegInfinity = (float.NegativeInfinity == double.NegativeInfinity); //true  bool isNanEqual = (float.NaN == double.NaN);  //false, WHY? 

Answer 1

NaN is never equal to NaN (even within the same type). Hence why the IsNaN function exists:

Double zero = 0; // This will return true. if (Double.IsNaN(0 / zero))  {     Console.WriteLine("Double.IsNan() can determine whether a value is not-a-number."); } 

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You should also be aware that none of the comparisons you've shown are actually occurring "as is". When you write floatValue == doubleValue, the floats will actually be implicitly converted to doubles before the comparison occurs.