StackOverflow2013

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copied!<p>You use a <code>*</code> when the variable type is a class.</p> <p>An example may help.</p> <pre><code>NSNumber *number; NSInteger integer; </code></pre> <p>The <code>NSNumber</code> variable type is a class while <code>NSInteger</code> is just another name for a normal C-type <code>int</code>. As you can see here, the compiler replaces every occurrence of <code>NSInteger</code> with <code>int</code>:</p> <pre><code>#if __LP64__ || NS_BUILD_32_LIKE_64 typedef long NSInteger; typedef unsigned long NSUInteger; #else typedef int NSInteger; typedef unsigned int NSUInteger; #endif </code></pre> <hr> <p>Further, you cannot declare an instance of a class(an object), like <code>NSNumber</code>, without using a pointer(thus you use a <code>*</code>). The reason for this is that when you <code>alloc</code> an instance of a class as an object a memory address is returned. A pointer is a type of variable that specifically refers to a memory location. For example:</p> <pre><code>NSNumber *number = [NSNumber alloc]; </code></pre> <p>Here <code>number</code>'s numeric value would be a memory location like <code>0x19a30c0</code>. You could operate on it by adding and subtracting, like an <code>int</code>. The key purpose of declaring it as a <code>NSNumber</code> pointer is so the compiler can help the coder verify that the class has certain methods or to access known properties.</p> <hr> <p>One last example:</p> <pre><code>NSInteger integer = [NSNumber alloc]; </code></pre> <p>What would the value of <code>integer</code> be? In our example, it would be 0x19a30c0. With this you could actually still access the newly allocated <code>NSNumber</code> object via <code>[integer someMethod]</code>. The compiler would give you a warning, though. More over:</p> <pre><code>integer += 4; </code></pre> <p>This would affect the numeric value <code>0x19a30c0</code> by adding 4 to it and making it <code>0x19a30c4</code>.</p> <hr> <p>Look at this Wikipedia article on <a href="http://en.wikipedia.org/wiki/Pointer_(computing)#C_and_C.2B.2B" rel="nofollow noreferrer">C/C++ pointers</a> for some more examples of how, when, and why to use an <code>*</code> operator.</p>

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