How do I take, then change to string when...

[MiserableMad]

What I want to do is take the character that the user inputs, adds that to a string and change the character to specified one that I define. I know how I am going to accomplish that. I am using a text changed sub(). But the problem is when I change the character in the sub() it loops through the process.

Text_changed
 
dim a as string
if text.text.substring(text.text.length -1 ) = "a" then
a &= "a"
text.text &= "1"
exit sub