Compilare: user.cpp: In function ‘std::__cxx11::string reversepolishnotation(char*)’: user.cpp:34:17: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i = 0;i< strlen(exp);i++) ~^~~~~~~~~~~~~ user.cpp: In function ‘int value(std::__cxx11::string)’: user.cpp:97:18: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i=0;i<postfix.size();i++) ~^~~~~~~~~~~~~~~ user.cpp:101:32: warning: array subscript has type ‘char’ [-Wchar-subscripts] S.push(V[postfix[i]]); ^ user.cpp:95:9: warning: unused variable ‘answer’ [-Wunused-variable] int answer=0; ^~~~~~ user.cpp: In function ‘int main()’: user.cpp:137:12: warning: array subscript has type ‘char’ [-Wchar-subscripts] V[c]=1-V[c]; ^ user.cpp:137:19: warning: array subscript has type ‘char’ [-Wchar-subscripts] V[c]=1-V[c]; ^ user.cpp: In function ‘int val(int, int, char)’: user.cpp:92:1: warning: control reaches end of non-void function [-Wreturn-type] } ^