/in/foo.cc: In function 'int bfs(int, int)':
/in/foo.cc:33:1: warning: no return statement in function returning non-void [-Wreturn-type]
 }
 ^
/in/foo.cc: In function 'int main()':
/in/foo.cc:39:10: warning: unused variable 'c' [-Wunused-variable]
     char c;
          ^
/in/foo.cc:37:20: warning: iteration 499 invokes undefined behavior [-Waggressive-loop-optimizations]
             f[i][j]=10000;//把f数组赋一个很大的值
             ~~~~~~~^~~~~~
/in/foo.cc:36:23: note: within this loop
         for(int j=1; j<=500; j++)
                      ~^~~~~