While-Loop works but not the if statement?

Question

I have this while loop in my code. The loop seems to work fine since I printed my i++ in the console. But for some reason it only checks my if statement the first time around. I can only add one title into the NSMutableArray called sectionZeroTitleArray. I have many arrays in this loop so it might get confusing. I will try my best to explain.

Here is what I am trying to do: Loop through the length of an array(topicArray). If the array's(topicArray)is the same as this other array's(anotherArray) first object then add an object that has the same index(titleArray) as topicArray to a new MutableArray(sectionZeroTitleArray).

I'm sure I did something stupid, maybe someone that hasn't stared at this all day can fix me up? Please and thank you.

while (i < (topicArray.count)) {
  if ([topicArray objectAtIndex:i] == [anotherArray objectAtIndex:0]) {
   [sectionZeroTitleArray addObject:[titleArray objectAtIndex:i]];
  }
  NSLog(@"sectionZeroLoopCount: %d", i);
  i++;
 }

Add the following before the if statement: NSLog(@"topicArray value:%@, anotherArray value:%@", [topicArray objectAtIndex:1], [anotherArray objectAtIndex:0]); — Kris Markel
– Kris Markel, Commented Sep 28, 2010 at 23:00
Does your topicArray contain the exact same object twice? If not, it's quite natural, that it goes only once into the if-brackets. Sure, you don't mean "objectAtIndex:i"? — Philipp Schlösser
– Philipp Schlösser, Commented Sep 28, 2010 at 23:00
Also, what are the types of the objects stored in the arrays? Often, you want to use isEqual: or isEqualToString: rather than ==. — Kris Markel
– Kris Markel, Commented Sep 28, 2010 at 23:01
You have to define what you mean by "is the same as" means. Right now you have written == which means that the pointers point to the same object (the pointers have the same value). — vakio
– vakio, Commented Sep 28, 2010 at 23:07
DUDE, you guys are sick, lol I posted like 5 mins ago and everyone already have the answer. I love this community and you guys are all awesome. If I could, I would give you all check marks. — slowman21
– slowman21, Commented Sep 28, 2010 at 23:09

Jacob Relkin · Accepted Answer · 2010-09-28 22:56:47Z

5

You are checking for pointer equality when you use ==. Are you sure you want to do this? What is the type that you're expecting? If it's a NSString, use isEqualToString:, otherwise use NSObject's isEqual: method:

If the expected type is an NSString:

if([[topicArray objectAtIndex:i] isEqualToString:[anotherArray objectAtIndex:0]]) {
   //...
}

Otherwise, you should probably do this:

if([[topicArray objectAtIndex:i] isEqual:[anotherArray objectAtIndex:0]]) {
   //...
}

answered Sep 28, 2010 at 22:56

Jacob Relkin

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Comments

jer · Accepted Answer · 2010-09-28 22:57:10Z

1

Yeah, you're comparing the pointers and not the values. Look at the documentation of NSString, particular the isEqualToString: method for comparing strings.

answered Sep 28, 2010 at 22:57

jer

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