iphone Development - adding a loop?

Question

Hello,i need help create a loop that check if the item selected in the array is already picked before, if yes randomize it again. implement in this function:

-(NSString*) randomBallPick:(NSString*) Filename
{
    NSMutableArray *imageArray = [[NSMutableArray alloc] init];
    for (int c=0;c<37;c++)
    {
     NSString *imageName = [NSString stringWithFormat:@"image_%d.png", c];
     [imageArray addObject: imageName];
    }
    int numFileNames = [imageArray count];
    int chosen = arc4random() % numFileNames;
    Filename = [imageArray objectAtIndex: chosen];
    return Filename;
    [imageArray release];
}

Answer 1

You'll need somewhere to store whether a particular ball has already been selected.

Once you pick a ball, if it's been selected before, go back to the start of the function and try again.

Note that this probably isn't the best way to handle it - once you get down to where there are only a handful of not-yet-picked balls in the array, you'll spend a lot of time re-picking until you get a new one. A better way would be to maintain a list of not-yet-picked balls, and splice them out of the list as they get picked.

EDIT: psuedocode version of the loop-until-we've-found-it method. You'll need to implement getIt() and Foo::hasNotBeenPickedYet(), as well as translate it into actual code.

Foo foo = null;
while(!foo) {
    Foo temp = getIt();
    if(temp.hasNotBeenPickedYet())
        foo = temp;
}
return foo;

Answer 2

I answered your other question about this function: Here's the answer from there modified to only return file names that haven't been returned yet:

- (NSString*)randomBallPick
{
    static NSMutableArray *imageArray;

    if (!imageArray) {
        imageArray = [[NSMutableArray alloc] init];
        for (int c = 0; c < 37; c++)
        {
            NSString *imageName = [NSString stringWithFormat:@"ball_%d.png", c];
            [imageArray addObject:imageName];
        }
    }

    //pick one filename
    NSUInteger numFileNames = [imageArray count];
    if (numFileNames < 1) {
        return nil; // or handle this case in some other way
    }
    NSUInteger chosen = arc4random() % numFileNames;
    NSString *chosenFilename = [imageArray objectAtIndex:chosen];
    [imageArray removeObjectAtIndex:chosen];
    return chosenFilename;
}

Basically, when it returns one of the file names, it also removes it from imageArray.

Of course, once imageArray is empty (numFileNames < 1) the above returns nil. Not sure if that's appropriate and you might need to handle that case differently.