Compilare: user.cpp: In function ‘void Postfix(const string&)’: user.cpp:21:37: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 0; i < expr.length(); ++i) ^ user.cpp: In function ‘int calculate()’: user.cpp:62:33: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 0 ; i < G.size(); ++i) ^ user.cpp: In function ‘int getPrioritate(char)’: user.cpp:13:1: warning: control reaches end of non-void function [-Wreturn-type] } ^