Question: Is there a way in Eclipse to easily find all appearances of a variable in a file without having to manually search (CTRL + F) for it?

Answer: 
There is a search with many features accessible with `Control`+`G`, but it does not support variables inside of a function.

There is also another search, which occurs when you select a variable or other thing and press `Control`+`Shift`+`G`.
In case you want to find all occurrences of variable to rename it, you can do it using `Alt`+`Shift`+`R`.