/in/foo.c: In function 'main':
/in/foo.c:15:28: error: 'M_PI' undeclared (first use in this function)
   15 |         float theta = 72 * M_PI / 180.0;
      |                            ^~~~
/in/foo.c:15:28: note: each undeclared identifier is reported only once for each function it appears in
/in/foo.c:17:18: warning: implicit declaration of function 'abs' [-Wimplicit-function-declaration]
   17 |         float m=(abs(a[1]-b[1]))/l,n=(abs(a[0]-b[0]))/l;
      |                  ^~~
/in/foo.c:3:1: note: include '<stdlib.h>' or provide a declaration of 'abs'
    2 | #include<math.h>
  +++ |+#include <stdlib.h>
    3 | int square(int x)