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

You can either use NAN macro, or simply one of nan/nanf functions to assign a nan value to a variable.
to check if you are dealing with a nan value, you can use isnan(). Here is an example:

#include 
#include 

int main(void) {

    float a = NAN;//using the macro in math.h
    float f = nanf("");//using the function version 
    double d = nan("");//same as above but for doubles!

    printf("a = %f\nf = %f\nd = %f\n",a,f,d);

    if(isnan(a))
        puts("a is a not a number!(NAN)\n");

    return 0;
}

Running the code snippet above will give you this output:

a = nan
f = nan
d = nan
a is a not a number!(NAN)

Run the code yourself : http://ideone.com/WWZBl8
read more information : http://www.cplusplus.com/reference/cmath/NAN/