lcd programming

I want to see a code that takes an input, from an LCD and is used in the code.
Imagine I have an LCD and I am using it to set the temp.
How do I code so that the number on the LCD tells arduino to respond?
I know how to code to make the LCD number change.
I am trying to code so that a consumer can set a temp using a up and down button that also shows the set temp on an LCD.
This has had to be done before.
Anyone there can just show me the code?
Its got to be simple. I tend to overthink these things.

dawast:
Imagine I have an LCD and I am using it to set the temp.

No, I can't imagine. What I can imagine is you set the temperature by sensible means, and the LCD indicates that setting.