Compilare: user.cpp: In function ‘int main()’: user.cpp:18:17: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while(top < v.size()) { ~~~~^~~~~~~~~~ user.cpp:10:34: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("undo2.in", "r", stdin); ^ user.cpp:11:36: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("undo2.out", "w", stdout); ^ user.cpp:12:18: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%d", &n); ^ user.cpp:16:26: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%d%d", &q, &x); ^