/in/foo.cc: In function 'void bfs(int, int)':
/in/foo.cc:24:48: warning: statement has no effect [-Wunused-value]
  hx[tail]=xx;hy[tail]=yy;step[tail]=0;a[xx][yy]=='1';
                                       ~~~~~~~~~^~~~~
/in/foo.cc:39:14: warning: statement has no effect [-Wunused-value]
     a[tx][ty]=='1';
     ~~~~~~~~~^~~~~