General :: Exit Bash Script - Add - Del - Edit User From Certain File Using Different CASE Variables

I have made a simple bash script through which i can add, del, edit user from certain file using different CASE variables. like
case
1. adduser
2. del user
3. edit user

Now i want to add a exit CASE like
1. adduser
2. del user
3. edit user
4. exit

Now i want to make a script such a way that, if user input is 4 then only script quit. I used with exit function also but it didn't work. if user press ENTER or other keys then also it quit the program.