Compilare: main.cpp: In function 'std::vector<std::__cxx11::basic_string<char> > convert_to_reverse_polish_notation(std::string)': main.cpp:25:22: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare] 25 | for(int i = 0; i < expression.size(); i++){ | ~~^~~~~~~~~~~~~~~~~~~ main.cpp:29:21: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare] 29 | while(i < expression.size() && isdigit(expression[i])){ | ~~^~~~~~~~~~~~~~~~~~~ main.cpp: In function 'int evaluate_expression(std::string)': main.cpp:65:22: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<std::__cxx11::basic_string<char> >::size_type' {aka 'long unsigned int'} [-Wsign-compare] 65 | for(int i = 0; i < postfix_expression.size(); i++){ | ~~^~~~~~~~~~~~~~~~~~~~~~~~~~~