Compilare: user.cpp: In function ‘int main()’: user.cpp:33:69: warning: operation on ‘nr’ may be undefined [-Wsequence-point] stiva[++nr] = (stiva[nr - 1] * 2 + (sir[i] - '0')) % mod; ^ user.cpp:87:87: warning: operation on ‘nr’ may be undefined [-Wsequence-point] stiva[++nr] = ((long long)1LL * stiva[nr - 1] * 10 + (sir[i] - '0')) % mod; ^ user.cpp:11:35: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen ("twosets.in", "r", stdin); ^ user.cpp:12:37: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen ("twosets.out", "w", stdout); ^ user.cpp:14:19: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf ("%d\n", &T); ^ user.cpp:19:19: warning: ignoring return value of ‘char* gets(char*)’, declared with attribute warn_unused_result [-Wunused-result] gets (sir + 1); ^ user.cpp:42:19: warning: ignoring return value of ‘char* gets(char*)’, declared with attribute warn_unused_result [-Wunused-result] gets (sir + 1); ^ /tmp/ccS8LaeF.o: In function `main': user.cpp:(.text.startup+0x90): warning: the `gets' function is dangerous and should not be used.