Question

I am trying to write a method for a new class called “word”, which is a subclass of NSString. I want a method that will accept a NSString containing a single character and return the the place within the word of every instance of that string. I have this so far:

@implementation Word
    -(NSMutableArray *)placeOfLetter: (NSString *)letterAsked;{
        NSUInteger *len=(NSUInteger *)[self length];
        int y=0;
        char letter=(char)letterAsked; 

        for (NSUInteger *x=0; x<len; x++) {
                if ([self characterAtIndex:*x]==letter){
                     [matchingLetters insertObject:x atIndex:y];
                     y++;
                }
        }
    }     
@end

however, xcode is telling me that I cannot put x as a the parameter for insertObject, because the “implicit conversion from NSUInteger to id is disallowed. How can I get around this?

Answer 1

The problem you’re encountering is stemming mostly from your treating NSUInteger as a pointer; you have some other casting problems as well. Try the following:

• Instead of taking a full string for the letterAsked argument, then getting a char out of it, just get a char (or unichar) as your argument to begin with. You avoid the letter = (char)letterAsked conversion altogether.

• Don’t make len a pointer. You may not need to declare len at all. Consider writing your for loop like:

  for(NSUInteger x = 0; x < [self length]; x++) { // ...
  

  This also helps you in the -characterAtIndex: call; you no longer need to dereference x in order to get the character.

• Like Hot Licks said in the comments, use an NSNumber if you want a position inside an NSArray; you need numbers to be class instances to go in an NSArray instance. You can create an NSNumber out of x like this:

  NSNumber * foundPosition = [NSNumber numberWithUnsignedInteger:x];
  

• Consider just using NSMutableArray’s -addObject: method, rather than keeping track of y and incrementing it each time. You’ll get the same result.