title: How to create an NSMutableArray of floating point values
body: <p>I'm new to Objective-C and iPhone development, and I'm trying to store floating-point values in an NSMutableArray, but when I do I get an error saying "incompatible type for argument 1 of 'addObject". What am I doing wrong?  I'm trying to create an array of doubles that I can perform math calculations with.</p>