M_PI flagged as undeclared identifier

Question

When I compile the code below, I got these error messages:

(Error  1   error C2065: \'M_PI\' : undeclared identifier 
2   IntelliSense: identifier \"M_PI\"          


        

Answer 1

math.h does not define M_PI by default.

So go with this:

#ifndef M_PI
    #define M_PI 3.14159265358979323846
#endif

This will handle both cases either your header have M_PI defined or not.