Why it's working wrongly?

Question

Why it's working wrongly?

https://code.sololearn.com/cDUwRaLnjIG5/?ref=app

In structures cin.getline,cin.get is not working.
But cin works finely.I replaced char array to string and I used getline but also that's not working why?

Answer 1

for(int i=0;i<n;i++)
{
fflush(stdin); // <= do this or cin.ignore();
cout<<"\nEnter Book Name : ";
cin.getline(b[i].bookname,20);
................
...............

Answer 2

cin.ignore() is works correctly.
But fflush(stdin) is not working and that's says error .why? what is fflush and cin.ignore explain please.