Question

what r non printing characters of open office writer.
PLEASE ANSWER ME FAST

Answer 1

non printing characters are those which do not appear on paper when we print a document. for example, space bar, enter , tab

Answer 2

And specifically the regular expressions you asked about are:
$ para. break
\n line break
\t tab

You can find nothing beyond a paragraph break so, for instance, $$ will not work. Also $ does not work in the Replace box. For unknown reasons there \n stands for a paragraph break and there is nothing that stands for a line break.