/in/foo.c:8:14: error: unknown type name 'point'
 double Cross(point A,point B,point C)
              ^~~~~
/in/foo.c:8:22: error: unknown type name 'point'
 double Cross(point A,point B,point C)
                      ^~~~~
/in/foo.c:8:30: error: unknown type name 'point'
 double Cross(point A,point B,point C)
                              ^~~~~
/in/foo.c:16:15: error: unknown type name 'point'
 void AddCross(point A,point B,point C,point D)
               ^~~~~
/in/foo.c:16:23: error: unknown type name 'point'
 void AddCross(point A,point B,point C,point D)
                       ^~~~~
/in/foo.c:16:31: error: unknown type name 'point'
 void AddCross(point A,point B,point C,point D)
                               ^~~~~
/in/foo.c:16:39: error: unknown type name 'point'
 void AddCross(point A,point B,point C,point D)
                                       ^~~~~
/in/foo.c:21:10: error: unknown type name 'point'
 void Cut(point A,point B)
          ^~~~~
/in/foo.c:21:18: error: unknown type name 'point'
 void Cut(point A,point B)
                  ^~~~~
/in/foo.c: In function 'main':
/in/foo.c:41:30: warning: implicit declaration of function 'Cut' [-Wimplicit-function-declaration]
         for(int i=1;i<m;i++) Cut(tmp[i],tmp[i+1]);
                              ^~~