foo.cc: In function 'int main()':
foo.cc:158:8: warning: this 'if' clause does not guard... [-Wmisleading-indentation]
   else if (change[x]);
        ^~
foo.cc:159:3: note: ...this statement, but the latter is misleadingly indented as if it were guarded by the 'if'
   {
   ^
foo.cc:25:6: warning: unused variable 'dir' [-Wunused-variable]
  int dir[4] = { -1,1,-m,m };
      ^~~
foo.cc:24:7: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
  scanf("%d%d", &n, &m);
  ~~~~~^~~~~~~~~~~~~~~~
foo.cc:40:7: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
  scanf("%d", &k);
  ~~~~~^~~~~~~~~~
foo.cc:44:8: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
   scanf("%d%d", &a, &b);
   ~~~~~^~~~~~~~~~~~~~~~

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