Compilare: main.cpp: In function 'int main()': main.cpp:22:20: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i=1; i<=n; ++i) ~^~~ main.cpp:26:20: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i=1; i<=n; ++i) ~^~~ main.cpp:18:34: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result] freopen("perm2.in","r",stdin); ^ main.cpp:19:36: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result] freopen("perm2.out","w",stdout); ^ main.cpp:21:21: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result] scanf("%lu", &n); ^ main.cpp:23:20: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result] scanf("%d", &a[i]); ^