foo.cc: In function 'int main()':
foo.cc:29:22: warning: array subscript has type 'char' [-Wchar-subscripts]
    maxcnt=cnt,shmax[k]=(char)i;
                      ^
foo.cc:31:13: warning: array subscript has type 'char' [-Wchar-subscripts]
    shmax[++k]=(char)i;
             ^
foo.cc:37:11: warning: array subscript has type 'char' [-Wchar-subscripts]
    shmax[k]=(char)i;
           ^
foo.cc:7:7: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
  scanf("%[^\n]",ch);
  ~~~~~^~~~~~~~~~~~~

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