How to produce a NaN float in c?

Question

float f = (float)\'a\';
if(f < 0){ 
}   
else if(f == 0){ 
}   
else if(f > 0){ 
}   
else{
    printf(\"NaN\\n\");                                                     


        

Answer 1

This works for constants too (0/0 will give a compiler error on vs):

const unsigned maxU = ~0;
const float qNan =  *((float*)&maxU);

Answer 2

To produce a nan, there are a few ways:

1) generate it manually (read ieee754 to set up the bits properly)

2) use a macro. GCC exposes a macro NAN. It's defined in math.h

The general way to check for a nan is to check if (f == f) (which should fail for nan values)

For nan, the exponent bits in the float representation should all be set to 1 (float consists of a signed bit, a set of exponent bits and a set of mantissa bits)

Answer 3

nan is produced when we program contain value like 0.0/0.0 as said by @Dan Cecile OR sqrt(-1).