how to debug runaway argument?

Question

How do I figure out what line the latex starts looking for a missing brace or..... I would prefer not to include my latex code

Excluding 'comment' comment.)

Runaway argument? ! File ended while scanning use of \next. \par <*> ./EvenCycleTransversal.tex

I suspect you have forgotten a }', causing me to read past where you wanted me to stop. I'll try to recover; but if the error is serious, you'd better type E' or `X' now and fix your file.

! Emergency stop. <*> ./EvenCycleTransversal.tex

*** (job aborted, no legal \end found)

p.s. what does the type E or X mean? how would I do that?

Answer 1

Answering the question as asked:

Tools to track mismatched brace errors:

• Insert \errorcontextlines=10, which is useful for clarifying many error messages
• Run with e-TeX (automatic for almost all cases) and insert tracinggroups=1 \tracingnesting=1
• Look in the log file

You are probably running TeX/LaTeX from within an editor, or an app, or on a website, so you can't interact with it. Run it by opening a terminal window and typing pdflatex myfile.tex, for example. Then, at each error, the run will pause for instructions. But they aren't very useful, except for "X" to exit without continuing. Typing "?" at the prompt gives you a list:

? ?
Type <return> to proceed, S to scroll future error messages,
R to run without stopping, Q to run quietly,
I to insert something, E to edit your file,
1 or ... or 9 to ignore the next 1 to 9 tokens of input,
H for help, X to quit.
? 

Note "Q" means "Quiet", not "Quit"; and "E" is unlikely to open the editor the way you want.