Compilation Error

Question

Soooo I've made a code that is pretty complex (for my standards) and after changing everything that resulted with an error I started the code aaaand... "compilation Error". So here is my question: What does it mean? And what I need to change to make it work?
Here is the link:
https://code.sololearn.com/cr8JFJp4bU0m/?ref=app
I really need this to work because I want to make a decimal to hexadecimal number changer and I've heard that it is the simplest way
EDIT: Thanks for answers now there is no compilation error left now I only need to fix the math in code and I'll work c:
EDIT 2: It works c:

Answer 1

The characters within your array should be enclosed in single quotes. Fixing that at least allows your code to be compiled.