Compilare: user.cpp: In function ‘int main()’: user.cpp:57:42: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int j = 0; j < strlen(sir) - 1; j++) ^ user.cpp: In member function ‘char Stack::pop()’: user.cpp:31:5: warning: control reaches end of non-void function [-Wreturn-type] } ^