Strange behaviour of macros C/C++

Question

I\'m using some macros, and observing some strange behaviour.

I\'ve defined PI as a constant, and then used it in macros to convert degrees to radians and radians to

Answer 1

Macros just do text substitution without regard for context, so what you wind up with is:

cout << "PI, in degrees: " << atan(1) * 4 * 180 / atan(1) * 4 << endl;

Note the distinct lack of parens around the second atan(1) * 4, causing it to divide only by atan(1) and then multiply by 4.

Instead, use inline functions and globals:

const double PI = atan(1) * 4;
double radians(double deg) { return deg * PI / 180; }
double degrees(double rad) { return rad * 180 / PI; }