When to use % and when to not

Question

I have recently falled into an error because I didn't use % when I was supposed to. My question is now: When do I have to use % at the end of the line and when should I leave it out?

Related Question: When is it harmful to add percent character at end of lines in a \newcommand, or similar. — Peter Grill, Jan 05 '17 at 06:42

score 8 · Accepted Answer · answered Oct 13 '15 at 23:15

8

An end of line is a space so your question is asking when to add a space.

foo
bar

is the same as

foo bar

but

foo%
bar

is the same as

foobar

so it just depends on the context. Sometimes a space is needed to separate words, or for TeX syntactic reasons, sometimes a space is not needed but ignored anyway, and sometimes a space is definitely wrong at that point.

answered Oct 13 '15 at 23:15

David Carlisle

757,742

...except for things like verbatim, where an EOL is not a space. – Steven B. Segletes Oct 13 '15 at 23:29
I also think it worth to explicitly mention that spaces (and thus %) are ignored after \if family of conditionals, as well as after \else and \fi...since they are used pervasively in macros. – Steven B. Segletes Oct 13 '15 at 23:32
@StevenB.Segletes ??? \if has no special treatment of spaces. – David Carlisle Oct 14 '15 at 06:53
Did I say that? Must have been my alter-ego. Need to adjust the meds. – Steven B. Segletes Oct 14 '15 at 10:00

When to use % and when to not

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