Compilare: main.cpp: In function 'int main()': main.cpp:37:17: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare] 37 | while(index < expression.size()){ | ~~~~~~^~~~~~~~~~~~~~~~~~~ main.cpp:41:25: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare] 41 | while(index < expression.size() && isDigit(expression.at(index))){ | ~~~~~~^~~~~~~~~~~~~~~~~~~