Compilare: main.cpp: In function 'int evaluate(std::string)': main.cpp:43:23: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare] 43 | for (int i = 0; i < expr.size(); i++) { | ~~^~~~~~~~~~~~~ main.cpp:50:22: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare] 50 | while (i < expr.size() && isdigit(expr[i])) { | ~~^~~~~~~~~~~~~