'What's the difference between "pi" and "M_PI" in objc

Including some math in my code I stumbled over the constant "PI". At least in my Xcode version 4.6 I could use either one. But what is the difference between pi and M_PI? The documentation is little bit tight on that topic.



Sources

This article follows the attribution requirements of Stack Overflow and is licensed under CC BY-SA 3.0.

Source: Stack Overflow

Solution Source