I knew double or float value can be not only normal value(-1.3, 0, 1.0, 2.3) but also NAN and INFINITY in Objective-C.
Is there other special values except for NAN and INFINITY for double/float value in Objective-C?
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Primitive types in Objective-C are covered by the C standard, since ObjC is an OOP system grafted to C.
Which transforms your question to "What special values are there for float/doubles in C?"
Most (if not all) compilers will generate float and double arithmetic that conforms to IEEE 754. In this standard, there are 2 types of NaNs (signalling and quiet), 2 infinities (+Infinity, -Infinity) and finite numbers (which include signed zeros, +0 and -0). The topic is too wide to even start, and you'd do yourself a favor by reading a book about floating point arithmetic.
However the C language standard (before C99) does not make any guarantees for conformance to IEEE 754 and this is only a de-facto standard.
Also, in C you check for NaN values with the