Compilare: main.cpp: In function 'int eval(std::string&)': main.cpp:38:23: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare] 38 | for (int i = 0; i < expr.size(); i++) { | ~~^~~~~~~~~~~~~ main.cpp:41:22: 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 (i < expr.size() && expr[i] >= '0' && expr[i] < '9') | ~~^~~~~~~~~~~~~