Compilare: user.cpp: In function ‘int main()’: user.cpp:49:44: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(i = 0; s[i] != '\0' && sol.size() < ans; ++i) ^ user.cpp:31:36: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("brackets.in", "r", stdin); ^ user.cpp:32:38: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("brackets.out", "w", stdout); ^