Compilare: main.cpp: In function 'int extractNumber(std::__cxx11::string)': main.cpp:17:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i = 0; i < str.size(); i++){ ~~^~~~~~~~~~~~ main.cpp: In function 'int main()': main.cpp:35:21: warning: unused variable 'x' [-Wunused-variable] int x; ^