Compilare: main.cpp: In function 'int main()': main.cpp:36:21: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 1; i <= s.size(); i++) ~~^~~~~~~~~~~ main.cpp:39:21: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 0; i < s.size(); i++) { ~~^~~~~~~~~~ main.cpp:40:36: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if ((s[i] - '0') % 4 == 0 && k == s.size() - 1) { ~~^~~~~~~~~~~~~~~