Add 1 to a number in an NSString that contains characters Objective-C - objective-c

Question

I am new to learning Objective-C (my first programming language!) and trying to write a little program that will add 1 to a number contained within a string. E.g. AA1BB becomes AA2BB.
.
So far I have tried to extract the number and add 1. Then extract the letters and add everything back together in a new string. I have had some success but can't manage to get back to the original arrangement of the initial string.
The code I have so far gives a result of 2BB and disregards the characters before the number which is not what I am after (the result I am trying for with this example would be AA2BB). I can't figure out why!
NSString* aString = #"AA1BB";
NSCharacterSet *numberCharset = [NSCharacterSet characterSetWithCharactersInString:#"0123456789-"]; //Creating a set of Characters object//
NSScanner *theScanner = [NSScanner scannerWithString:aString];
int someNumbers = 0;
while (![theScanner isAtEnd]) {
// Remove Letters
[theScanner scanUpToCharactersFromSet:numberCharset
intoString:NULL];
if ([theScanner scanInt:&someNumbers]) {}
}
NSCharacterSet *letterCharset = [NSCharacterSet characterSetWithCharactersInString:#"ABCDEFGHIJKLMNOPQRSTUVWXYZ"];
NSScanner *letterScanner = [NSScanner scannerWithString:aString];
NSString* someLetters;
while (![letterScanner isAtEnd]) {
// Remove numbers
[letterScanner scanUpToCharactersFromSet:letterCharset
intoString:NULL];
if ([letterScanner scanCharactersFromSet:letterCharset intoString:&someLetters]) {}
}
++someNumbers; //adds +1 to the Number//
NSString *newString = [[NSString alloc]initWithFormat:#"%i%#", someNumbers, someLetters];
NSLog (#"String is now %#", newString);

Answer 1

This is an alternative solution with Regular Expression.
It finds the range of the integer (\\d+ is one or more digits), extracts it, increments it and replaces the value at the given range.
NSString* aString = #"AA1BB";
NSRange range = [aString rangeOfString:#"\\d+" options:NSRegularExpressionSearch];
if (range.location != NSNotFound) {
NSInteger numericValue = [aString substringWithRange:range].integerValue;
numericValue++;
aString = [aString stringByReplacingCharactersInRange:range withString:[NSString stringWithFormat:#"%ld", numericValue]];
}
NSLog(#"%#", aString);