Your title and example suggests that the question numbers are already correct, you just want to add a zero before them, and you say you have 325 questions; so I wonder, do you want:

01-
02-
...
09-
010-
011-
...
099-
0100-
0101-
...
0325-

which is what your question, taken precisely, says? Or:

001-
002-
...
009-
010-
011-
...
099-
100-
101-
...
325-

which is what I think @PeterJones assumed you meant?

Also, are the numbers themselves already correct (just missing the leading zeros), or do you need to renumber, too?

If all you wanted was to add one zero before every question number, and the pattern follows your example that all question lines, and only question lines, start with a number, then all you need is:

From the menu, select Search | Replace; in the dialog, set:

Find what : ^(\d)
Replace with: 0$1
Search Mode : Regular expression

and use the Replace All button.

Thnak you and thanks too for the FAQ`s!

In one step, with just Notepad++? No. Notepad++ cannot natively handle mathematical replacements, as explained in this FAQ (which contains some of the workarounds mentioned below).

If you allow for more than one step, or if you are willing to install a plugin, then yes.

Until recently, I would have recommended a multi-step process, similar to:

1. replace all newlines that don’t come before #- with a different character that you don’t use in your document, like a smiley face (\R(?!\d+-) ⇒ ☺)
2. delete all the numbers before the - at the beginning of each combined line (^\d+(?=-) ⇒ empty)
3. Use a column selection then Column Editor (Edit > Column Editor or Alt+C) to insert numbers starting at 1 with leading zeroes
4. change the different-character back into newline sequence (☺ ⇒ \r\n for Windows EOL)

But now that there are a couple of plugins that more easily handle mathy replacements, I’d suggest using one of those.

For the Columns++ plugin, I am pretty sure that something like the following (derived from this FAQ section would work with Columns++ (and the author @Coises will correct me if I’m wrong):

• Using the plugin’s search/replace (not Notepad++ search/replace)
  FIND = ^\d+-
  REPLACE = (?=3:match)-
  • where the 3 in that replacement means it will be three digits (001 - 325)
  • and the match in that replacement means

And in the MultiReplace plugin, I think you would need to use the CNT variable in its search/replace feature.

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