Given an array of strings, e.g.: NSArray * files = @"[@"file2", @"folder22", @"folder10", @"file1", @"folder100", … … …, nil]; Describe how you would write some kind of method or function that would sort the strings in a predictable manner (e.g. "file1", "file2", "folder2", "folder10", "folder100" instead of "folder10", "folder100", "folder2")

ObjCFileNameSorting

- (NSComparisonResult)fileNameCompare:(NSString *)aString
{
    NSComparisonResult result;
    
    // split string1 and string2 each into two halves
    //
    // then compare string1 and string2's halves with each other

    NSString * firstHalfOfSelf = [NSString getFirstHalfOf: self];
    NSString * firstHalfOfOtherString = [NSString getFirstHalfOf: aString];
    
    result = [firstHalfOfSelf compare: firstHalfOfOtherString];
    if(result == NSOrderedSame)
    {
        NSString * secondHalfOfSelf = [NSString getSecondHalfOf: self];
        NSString * secondHalfOfOtherString = [NSString getSecondHalfOf: aString];
     
        NSInteger selfValue = [secondHalfOfSelf integerValue];
        NSInteger otherStringValue = [secondHalfOfOtherString integerValue];
        
        if(selfValue > otherStringValue)
        {
            result = NSOrderedDescending;
        } else {
            if(selfValue == otherStringValue)
            {
                result = NSOrderedSame;
            } else {
                result = NSOrderedAscending;
            }
        }
    }
    return(result);
}

// these methods pretty much assume that all input strings
// are in the form of letters + numbers (e.g. "abcdef1234")
//
// proper production code would do more error checking

+ (NSString *) getFirstHalfOf: (NSString *) someString
{
    NSString * stringToReturn;
    
    // create substring up to (but not including) the numeric portion of the name
    NSRange firstNumberCharacter = [someString rangeOfCharacterFromSet: [NSCharacterSet decimalDigitCharacterSet]];
    if(firstNumberCharacter.location != NSNotFound)
    {
        stringToReturn = [someString substringToIndex: firstNumberCharacter.location];
    } else {
        stringToReturn = someString;
    }
    return(stringToReturn);
}

+ (NSString *) getSecondHalfOf: (NSString *) someString
{
    NSString * stringToReturn;
    
    // create substring starting with the numeric portion of the name
    NSRange firstNumberCharacter = [someString rangeOfCharacterFromSet: [NSCharacterSet decimalDigitCharacterSet]];
    if(firstNumberCharacter.location != NSNotFound)
    {
        stringToReturn = [someString substringFromIndex: firstNumberCharacter.location];
    } else {
        stringToReturn = someString;
    }
    return(stringToReturn);
}

And yes, after I typed all this code out... I was informed that the best answer is simply that the NSString method "compare: options:" has an option of NSNumericSearch that does exactly what I needed to do.