newProgrammer:please help with insertString!

NSStrings cannot be changed once created. You must use a NSMutableString (creating it if required).

Edit: just seen you have attempted to use an NSMutableString but you have done it wrong. The split creates an array of NSString objects. You cannot cast them to NSMutableString: you are casting the wrong way. You can cast a subclass (NSMutableString) to a superclass (NSString) but not the other way. You need to create a new mutable object.

 

Another option would be to use NSString's stringByAppendingString f.e. by replacing the last two lines of your code with:

NSString *f = [[NSString stringWithString"00000000"] stringByAppendingString:[splitInput objectAtIndex:1]];

and work from there.
Just a thought.

 

The unwieldy and redundant [NSString stringWithString"00000000"] is redundant and unwieldy.

Replace it with @"00000000" and it works as well.

That's because @"anything" is an actual NSString object, and it responds to the same messages as any NSString does:

Code:

NSString *f = [@"00000000" stringByAppendingString:[splitInput objectAtIndex:1]];

This code is also redundant. First, temp doesn't need to be mutable. None of the operations or expressions it participates in have any need to modify it. In particular, splitting it does not require a mutable string.

Therefore, this expression yields a suitable string:

Code:

NSMutableString *temp =[firstNumber stringValue];

Even without knowing what type firstNumber is.

And this code is redundant for the same reason:

Code:

NSArray *splitInput = [[NSArray alloc]initWithArray:[temp componentsSeparatedByString:@"x"]];

It's unnecessary to alloc and init an entire new IMMUTABLE NSArray, when the one returned by componentsSeparatedByString meets every need. Furthermore, the alloc'ed array is leaking, because you own it but haven't released it. An array from componentsSeparatedByString is NOT owned, so WON'T leak when NOT released.