foo.cc: In function 'int main()':
foo.cc:15:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i=0;i<s.size();i++){
              ~^~~~~~~~~
foo.cc:16:12: warning: array subscript has type 'char' [-Wchar-subscripts]
   if(b[s[i]]){
            ^
foo.cc:17:16: warning: array subscript has type 'char' [-Wchar-subscripts]
    if(!b[s[i-1]])hz+='.'; 
                ^
foo.cc:18:13: warning: array subscript has type 'char' [-Wchar-subscripts]
    if(b[s[i]]==1)a.push(s[i]);
             ^
foo.cc:19:18: warning: array subscript has type 'char' [-Wchar-subscripts]
    else if(b[s[i]]==5){
                  ^
foo.cc:29:33: warning: array subscript has type 'char' [-Wchar-subscripts]
      while(!a.empty()&&b[a.top()]>=b[s[i]]){
                                 ^
foo.cc:29:42: warning: array subscript has type 'char' [-Wchar-subscripts]
      while(!a.empty()&&b[a.top()]>=b[s[i]]){
                                          ^
foo.cc:48:15: warning: operation on 'top' may be undefined [-Wsequence-point]
    case '^':z[--top]=pow(z[top-1],z[top+1]);break;
               ^~~~~
foo.cc:48:15: warning: operation on 'top' may be undefined [-Wsequence-point]
foo.cc:49:15: warning: operation on 'top' may be undefined [-Wsequence-point]
    case '+':z[--top]+=z[top+1];break;
               ^~~~~
foo.cc:50:15: warning: operation on 'top' may be undefined [-Wsequence-point]
    case '-':z[--top]-=z[top+1];break;
               ^~~~~
foo.cc:51:15: warning: operation on 'top' may be undefined [-Wsequence-point]
    case '/':z[--top]/=z[top+1];break;
               ^~~~~
foo.cc:52:15: warning: operation on 'top' may be undefined [-Wsequence-point]
    case '*':z[--top]*=z[top+1];break;
               ^~~~~
foo.cc:44:6: warning: unused variable 'len' [-Wunused-variable]
  int len=s.size();
      ^~~
foo.cc:45:20: warning: unused variable 'y' [-Wunused-variable]
  int i=0,top=0,x=0,y=0;
                    ^

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