/in/foo.cc: In function 'int bfs()':
/in/foo.cc:13:39: warning: unused variable 'a' [-Wunused-variable]
  int head=0, tail=1, x, y, i, j, cnt, a=0, b=0, l=0, r=0;
                                       ^
/in/foo.cc:13:44: warning: unused variable 'b' [-Wunused-variable]
  int head=0, tail=1, x, y, i, j, cnt, a=0, b=0, l=0, r=0;
                                            ^
/in/foo.cc:13:49: warning: unused variable 'l' [-Wunused-variable]
  int head=0, tail=1, x, y, i, j, cnt, a=0, b=0, l=0, r=0;
                                                 ^
/in/foo.cc:13:54: warning: unused variable 'r' [-Wunused-variable]
  int head=0, tail=1, x, y, i, j, cnt, a=0, b=0, l=0, r=0;
                                                      ^
/in/foo.cc:59:1: warning: control reaches end of non-void function [-Wreturn-type]
 }
 ^
/in/foo.cc:51:34: warning: 'new_d' may be used uninitialized in this function [-Wmaybe-uninitialized]
                         if( new_d==d || d=='0' ) //方向一致，或是目前是从起点刚出发 
                             ~~~~~^~~