How do you increase a number *directly* under the cursor?

Question

In vim et al, you can increase or decrease the number your cursor is on by using CTRLA and CTRLX. However, this increases the whole number but I would like to simply increase the number directly under the cursor. It's a little hard to describe so here's what I mean:

Ctrl+A usage, cursor is over the "6":
[6]5 -> 66

What I need:
[6]5 -> 75

or:
3[8]90 -> 3990

I hope that makes sense.

I've googled a bit but I'm not sure if such a shortcut exists so any tips are much appreciated!

Answer 1

<C-a> and <C-x> work on whole numbers (1 or more digits) but not on "parts" of a number. However it takes a "count" so 10<C-a> turns [6]5 into 75.

Another option, since you only want to change one digit, would be to do r7 to turn [6]5 into 75.

Answer 2

In this case, I usually type r and then the digit I want.