If... Then... Statements

I'm new to VBScript so bear with me...
 
Is there a way I can write if... then... statements and after saving the script as a .vbs file and not having to use the infobox to type in the words? For example:
 
Do
a=inputbox ("Example")
if a = "z" then
msgbox ("Z is the last letter of the alphabet.")
End if
Loop until a = "exit"
 
I want to make it so instead of typing "z" into the inputbox to make "Z is the last letter of the alphabet." pop up in a separate messagebox, I can just type "z" into a notepad window, hit enter, and the resulting "Z is the last letter of the alphabet." statement will pop up in the same window. Is this possible? Sorry if this is kind of hard to understand. I greatly appreciate any feedback.