Compilare: main.cpp: In member function 'ftype& ftype::operator+=(const ftype&)': main.cpp:39:71: warning: no return statement in function returning non-void [-Wreturn-type] ftype& operator +=(const ftype &a) { if((x += a.x) >= MOD) x -= MOD; } ^ main.cpp: In member function 'ftype& ftype::operator-=(const ftype&)': main.cpp:40:68: warning: no return statement in function returning non-void [-Wreturn-type] ftype& operator -=(const ftype &a) { if((x -= a.x) < 0) x += MOD; } ^ main.cpp: In member function 'ftype& ftype::operator*=(const ftype&)': main.cpp:41:66: warning: no return statement in function returning non-void [-Wreturn-type] ftype& operator *=(const ftype &a) { x = (1LL * x * a.x) % MOD; } ^ main.cpp: In member function 'ftype& ftype::operator/=(const ftype&)': main.cpp:42:76: warning: no return statement in function returning non-void [-Wreturn-type] ftype& operator /=(const ftype &a) { *this = (*this) * getPw(a, MOD - 2); } ^ main.cpp: In function 'std::vector<ftype> multiply(const std::vector<ftype>&, const std::vector<ftype>&)': main.cpp:135:19: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i = 0; i < a.size(); ++i) na[i] = a[i]; ~~^~~~~~~~~~ main.cpp:136:19: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i = 0; i < b.size(); ++i) nb[i] = b[i]; ~~^~~~~~~~~~ main.cpp:145:19: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i = 0; i < va.size(); ++i) { ~~^~~~~~~~~~~ main.cpp: In function 'int main()': main.cpp:202:16: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(i = 0; i < a.size(); ++i) if(a[i]) cout << i << ' ' << a[i] << '\n'; ~~^~~~~~~~~~