Assign values to NSMutable Array within for loop

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?

What you put into an NSMutableArray must be an Objective-C object. An int is not an object. An NSNumber is an object, if you wish to use that. Or you can use a regular C array of int. — Hot Licks
– Hot Licks, Commented Jul 16, 2012 at 17:06

Tim · Accepted Answer · 2012-07-16 17:14:43Z

2

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.

answered Jul 16, 2012 at 17:14

Tim

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3 Comments

esreli Over a year ago

NSNumber is a great class. Use it!

user1418214 Over a year ago

If I were to take these suggestions, would my parameter for -addObject: be foundPosition or (*foundPosition)? Wouldn't I be declaring found position as a pointer, and therefore need to dereference it?

Tim Over a year ago

Just foundPosition. It would be a pointer, yes, but all Objective-C objects are pointers - the compiler actually yells at you if you try to handle objects as static values in certain circumstances.

rob mayoff · Accepted Answer · 2012-07-16 17:15:24Z

1

NSUInteger is a typedef for either unsigned int or unsigned long, depending on your platform. It is not an object type. So when you declare NSUInteger *x=0, you're declaring x as a pointer-to-unsigned-integer, and initializing it to null.

The insertObject:atIndex: requires an NSUInteger, not an NSUInteger*, as its index argument.

Just take out the * from the for statement and the characterAtIndex: message.

You do have other problems in your method also, like casting letterAsked to a char instead of getting the character out of it using characterAtIndex: and declaring len as a pointer.

answered Jul 16, 2012 at 17:15

rob mayoff

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