Compilare: user.cpp: In function ‘bool check(int)’: user.cpp:30:26: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (i = X = 1; i <= N; X = (X * A + (++i) * B) % C) ^ user.cpp:34:26: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (i = X = 1; i <= N; X = (X * A + (++i) * B) % C) { ^ user.cpp:40:30: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if (last[X] == def + i) used--; ^ user.cpp: In function ‘int main()’: user.cpp:48:32: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("reg.in","r",stdin); ^ user.cpp:49:34: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("reg.out","w",stdout); ^ user.cpp:51:20: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%d", &t); ^ user.cpp:53:48: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%d%d%d%d%d", &A, &B, &C, &n, &k); ^