change do while into while... and initialize done = true instead of false. then when you press 5 (exit) change done = false to exit the loop...
int main ()
{
double checking, savings;
int choice;
get_balances (checking, savings);
bool done = true;
while(done) {
display_menu ();
cout << "Enter Choice: ";
cin >> choice;
switch (choice)
{
case TRANSFER:
transfer (checking, savings);
break;
case WITHDRAW:
withdraw (checking);
break;
case CHECK:
withdraw (checking);
break;
case DEPOSIT:
deposit (checking);
break;
case EXIT:
done = false;
break;
}
display_balances (checking, savings);
}
return 0;
}