foo.cc: In function 'int main()':
foo.cc:19:34: warning: operation on 'd' may be undefined [-Wsequence-point]
      if(a[i+dx[d]][j+dy[d]]!=0) d=(++d)%4;
                                 ~^~~~~~~~
foo.cc:25:3: warning: this 'for' clause does not guard... [-Wmisleading-indentation]
   for(j=1;j<=n;j++)
   ^~~
foo.cc:27:4: note: ...this statement, but the latter is misleadingly indented as if it were guarded by the 'for'
    cout<<endl;
    ^~~~

自豪的采用HydroJudge(https://github.com/hydro-dev/Hydro)进行评测。