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copied!<p>Suppose you have a class <code>MyClass</code> then by convention <code>nil</code> is used if you want to initialize its instance to null value (same as <code>null</code> in java) i.e.<br></p> <pre><code>MyClass *obj = nil; </code></pre> <p><br> and if you want to initialize a primitive pointer to null value (same as in c) you use <br></p> <pre><code>int *ptr = NULL; </code></pre> <p><br>and if you want to initialize to <code>Class</code> reference to null value (same as <code>null</code> in java) then use<br></p> <pre><code>Class classRefOfMyClass = Nil; </code></pre> <p>It's just a convention otherwise Nil or nil have same meaning and perhaps NULL , nil or Nil all are same.</p> <p>Here is the definition for these in <code>objc.h</code> file</p> <pre><code>#ifndef Nil # if __has_feature(cxx_nullptr) # define Nil nullptr # else # define Nil __DARWIN_NULL # endif #endif #ifndef nil # if __has_feature(cxx_nullptr) # define nil nullptr # else # define nil __DARWIN_NULL # endif #endif </code></pre> <p>And in <code>stddef.h</code></p> <pre><code>#define NULL ((void*)0) </code></pre> <p>And the definition of <code>__DARWIN_NULL</code> in <code>_types.h</code></p> <pre><code>#define __DARWIN_NULL ((void *)0) </code></pre> <p>So there is no difference logically. The main idea here is to initialize a pointer whether <code>C</code> or <code>Objective-C</code> to <code>0</code>. If you have knowledge of <code>C</code> then you can assign </p> <pre><code>int *ptr = 0; </code></pre> <p>without type casting <code>0</code> to a pointer. As you don't need to typecast <code>0</code> to assign it to a pointer.</p> <h1>In short they all are <code>0</code> and nothing else.</h1>

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