Saving part of found term when replacing in Notepad++

Question

I want to use Notepad++ to find/replace large chunks of code, but a hefty part of it deals with arrays. How can I put a "variable" in Notepad++'s Find/Replace window so that part of it can be saved and not overwritten?

The below example isn't perfect, as it could be converted using two simple find/replace searches, but I'd like to do something to the effect of Find: o[*] and Replace: p*.

Example

Original:

Or(a=o[0]);
Or(a=o[1]);
Or(a=o[2]);
Or(a=o[3]);
Or(a=o[4]);

What I need:

Or(a=p0);
Or(a=p1);
Or(a=p2);
Or(a=p3);
Or(a=p4);

Answer 1

If you enable the Regular expression radio button, you can use parenthesis to hold values.

Whatever is contained within the first () gets stored in \1, the second in \2 and so on.

Here's a basic illustration of that for your example.

The \d matches a digit. [ and ] have to be escaped with \ because they are special characters.