/in/foo.cc: In function 'int main()':
/in/foo.cc:83:21: warning: array subscript has type 'char' [-Wchar-subscripts]
        if(first[a[i]]>first[s2.top()])//高优先级直接入栈 
                     ^
/in/foo.cc:87:36: warning: array subscript has type 'char' [-Wchar-subscripts]
       while(!s2.empty()&&first[a[i]]<=first[s2.top()]&&s2.top()!='('){
                                    ^
/in/foo.cc: In function 'int com(int, int, char)':
/in/foo.cc:27:9: warning: 'tmp' may be used uninitialized in this function [-Wmaybe-uninitialized]
  return tmp;
         ^~~