NAME

       ALLEGRO_PI - Allegro 5 API

SYNOPSIS

              #include <allegro5/allegro.h>

              #define ALLEGRO_PI        3.14159265358979323846

DESCRIPTION

       C99 compilers have no predefined value like M_PI for the constant π, but you can use this one instead.

Allegro reference manual                                                                     ALLEGRO_PI(3alleg5)