how do i know its an EOF?
Depends on the language and how you read from the file. You neglected to mention what language you are using....on a programming question.
You can always find out how to determine EOF on your own. The languages and their standard libraries are documented. That means you can just Google up the documentation and read how to detect EOF.
Once you figure out the logic to detecting an EOF, obviously write the appropriate code for it.
and how should i put it if its the EOL char and i want the reader to go down to the next line?
Lines are nothing but blocks of text marked at the end by a newline character. The reader has no concept of "down". Computers are not humans. They don't open up a file on Microsoft windows and stare at a monitor. They see a continous stream of bytes of the computer, and interpret them as you tell them to.
- This is a line.\nThis is another line.\n\nNow a new paragraph.\nWith a second line.\nEOF
There's 86 "characters" on that example above. But you would actually omit the '\n' newline characters and EOF from your calculation.
But again, the actual logic you need to code depends on the language and what I/O functions you use to read the file.