How to add two strings together?

[yoran]

How do I add two strings together?
I have:
filename 'name' (don't know if it's zero terminated)
and
extension '.txt',0

How do I add these two together?

[debs3759]

Strictly speaking, you want to concatenate two strings, not add them. You need to create a variable long enough to hold both strings, then add them in the right order. If you still need help, post what you have so we can see what you don't understand.