I'm kinda new to Pine, but I have some experience with other languages.
I just wanted to make my own complete indicator instead of using 10 different EMAs, etc.
Instead, what happened was after literally declaring "X" one line before my code it still says that "X" is undeclared?
You are using mixed syntax from different versions of pinescript.
if you do not define the version, it will automatically use the pinescript version 1, and input.integer argument definition was introduced only in later versions.
To define a pinescript version simply add this line at the beginning of the script (4 is the latest one):
//@version=4
