Compilare: main.cpp: In function 'int main()': main.cpp:30:27: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 1; i < s.size() - 1; ++i) { ~~^~~~~~~~~~~~~~ main.cpp:46:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 0; i < s.size(); ++i) { ~~^~~~~~~~~~ main.cpp:21:38: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result] freopen("charlie.in", "r", stdin); ^ main.cpp:22:40: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result] freopen("charlie.out", "w", stdout); ^