Compilare: user.cpp: In function ‘void add_hash(int)’: user.cpp:24:38: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i = 0 ; i < a[hash].size(); ++i) ^ user.cpp: In function ‘int find_hash(int)’: user.cpp:39:38: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i = 0 ; i < a[hash].size(); ++i) ^ user.cpp: In function ‘int main(int, const char**)’: user.cpp:53:34: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("eqs.in", "r", stdin); ^ user.cpp:54:36: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("eqs.out", "w", stdout); ^ user.cpp:56:53: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%d %d %d %d %d", &a1, &a2, &a3, &a4, &a5); ^