Compilare: user.cpp: In function ‘bool check(long long unsigned int)’: user.cpp:13:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i = 1; i <= n; i++){ ^ user.cpp: In function ‘int main()’: user.cpp:24:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i = 1; i <= n; i++) in >> a[i].nd >> a[i].st; ^ user.cpp:31:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i = 1; i <= n; i++){ ^