The general documentation you should read is the "
String Programming Guide". It has sections on searching and scanning strings, as well as a lot of other stuff.
That guide should also be in the builtin Xcode documentation (use Xcode's Help menu to open the doc window, then search for String Programming Guide).
To solve the problem, Break It Down.
Step 1: How do you distinguish the number part of the text from the non-number part?
Maybe look at the NSCharacterSet class, and see what it has for identifying decimal digits. Then you'd be able to classify individual characters in the text as "part of a number" and "not part of a number".
Step 2: How do you access individual characters in the text, so they can be classified as "part of a number" and "not part of a number"?
See the NSString class, and look for methods that return a character at a specific index, or characters in a range.
Also look at NSString methods that let you scan and search an NSString for characters in an NSCharacterSet, and which returns the ranges of those characters.
Step 3: Having access to the ranges or individual characters of the text, and being able to distinguish number-parts from non-number-parts, you now have sufficient information to extract the parts that are the number-part and the non-number-part. Put each part into a separate NSString. Done.
Or see the NSScanner class. You should already be familiar with NSString and NSCharacterSet, or it won't make much sense.
The overall strategy is basic problem solving. Break it down, describe it in plain language, repeat. Keep applying that (breaking it down, describing it plainly), until you have clearly described problems that are easy enough to solve without further breaking them down.
Every program is an explanation. It explains to the computer exactly how to solve the problem. If you can't explain things, or don't understand what you're solving, or can't break things down, you won't be able to write programs.
