When is a float variable not equal to itself

Question

I was asked this questino on a programming test. The question was, I was passed in a float as a parameter, and asked when would the following code be false.

bool result  = (floatValue == floatValue);

I couldn't think of a valid reason or a situation of when this would be false and still can't. In the end, I answered that there will never be a case when this would be false. Was wondering if anyone can give me some example(s) of when this would be false

@M.M That's true when comparing two different float values, but in this case I think you're comparing one variable with itself. — 1201ProgramAlarm
– 1201ProgramAlarm, Commented Oct 2, 2015 at 4:37
@M.M. not sure I understand. floatValue here refers to the same lvalue. It's stored only once. — vsoftco
– vsoftco, Commented Oct 2, 2015 at 4:38

1201ProgramAlarm · Accepted Answer · 2015-10-02 03:51:09Z

12

floatValue == NaN

If floatValue is the result of a computation that is Not a Number, like 0/0.

answered Oct 2, 2015 at 3:51

1201ProgramAlarm

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2 Comments

dwnenr Over a year ago

OH. I was totally forgetting NaN. Does this also apply if floatValue is INF? Or is this just for when floatValue is NaN?

1201ProgramAlarm Over a year ago

Only for NaNs. Infinities compare normally (-infinity < any real number < +infinity; +infinity == +infinity; etc.).

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