Compilare: user.cpp: In function ‘int main()’: user.cpp:41:13: warning: array subscript has type ‘char’ [-Wchar-subscripts] ++f[buf[i]]; ^ user.cpp:45:22: warning: array subscript has type ‘char’ [-Wchar-subscripts] ++skipped[buf[head]]; --head; ^ user.cpp:48:21: warning: array subscript has type ‘char’ [-Wchar-subscripts] if (skipped[buf[i]]) { ^ user.cpp:49:20: warning: array subscript has type ‘char’ [-Wchar-subscripts] --skipped[buf[i]]; ^ user.cpp:35:29: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen(InFile, "r", stdin); ^ user.cpp:36:30: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen(OuFile, "w", stdout); ^ user.cpp:38:23: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%d%d", &N, &M); getchar(); ^ user.cpp:39:11: warning: ignoring return value of ‘char* gets(char*)’, declared with attribute warn_unused_result [-Wunused-result] gets(buf); ^ /tmp/ccQQmyLm.o: In function `main': user.cpp:(.text.startup+0x7f): warning: the `gets' function is dangerous and should not be used.