The problem is you didn't place cin.ignore in try_again() function
Code:
void try_again ()
{
char s;
cin >> s; //the cin is used to filter extra letters
cin.ignore();
if (s == 'y')
min ();
else if (s == 'n')
exit (0);
else
{
cout << "Please enter y, or n:";
try_again ();
}
}