The basic interpreter scans a line of code before executing it, so that the calculator won't freeze or worse.. If it encounters an error, it will stop executing the code, and tell you that an error occurred. It even tells you what kind of error it was, and in some cases there is an option that will take you to the error.
In TI-basic, error messages occur for a number of reasons.
1. Incorrect code 2. Not enough memory 3. Overflow 4. Non-real answers (negative root)
INCORRECT CODE The calculator says
ERR:SYNTAX 1.QUIT 2.GOTO
ERR:ARGUMENT 1.QUIT 2.GOTO
Option one quits from the program and returns you to the home screen.
Option two is more interesting; It takes you to the line of the program where the error occurred, So you can go fix it!