/in/foo.c: In function 'main':
/in/foo.c:68:25: warning: implicit declaration of function 'abs' [-Wimplicit-function-declaration]
   printf("%d %d\n",flag,abs(p-1)+abs(q-1));
                         ^~~
/in/foo.c:36:6: warning: unused variable 'a' [-Wunused-variable]
  int a[3][3];
      ^
/in/foo.c:35:8: warning: unused variable 'c' [-Wunused-variable]
  int b,c,n,i,flag,p/*行*/,q/*列*/;
        ^