Compilare: user.cpp: In function ‘std::string getCanonicalForm(std::string, int*)’: user.cpp:38:21: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while( i<E.size() ){ ^ user.cpp: In function ‘std::string getPostfixPolish(std::string)’: user.cpp:62:27: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for( int i=0;i<S.size();i++ ){ ^ user.cpp: In function ‘int evaluate(std::string, int*)’: user.cpp:105:26: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i=0;i<S.size();i++){ ^