Compilare: user.cpp: In member function 'virtual bool variable::evaluate()': user.cpp:43: warning: array subscript has type 'char' user.cpp: In function 'int main()': user.cpp:118: warning: comparison between signed and unsigned integer expressions user.cpp:123: warning: comparison between signed and unsigned integer expressions user.cpp:155: warning: array subscript has type 'char' user.cpp:155: warning: array subscript has type 'char' user.cpp: In member function 'virtual bool operation::evaluate()': user.cpp:19: warning: control reaches end of non-void function