Compilare: user.cpp: In function ‘bool check()’: user.cpp:19:31: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i=0; i<myset.size(); i++) ^ user.cpp: In function ‘int main()’: user.cpp:40:57: warning: operation on ‘last’ may be undefined [-Wsequence-point] st[++last] = (st[last-1]*2+a[i]-'0')%mod; ^ user.cpp:54:58: warning: operation on ‘last’ may be undefined [-Wsequence-point] st[++last] = (st[last-1]*10+a[i]-'0')%mod; ^ user.cpp:27:38: 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:28:40: 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:30:22: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%d\n", &t); ^ user.cpp:33:23: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%s", a); ^ user.cpp:47:23: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%s", a); ^