C++ syntax question, use of the class keyword
<p>Can any one explain "class X x;" what actually it mean ...in the program...Please give me some example also?
Ex:</p>

<pre><code>#include &lt;iostream&gt;
using namespace std;

class X {
    public:
        X() {}
};

class Y {
    public:
        Y() {}
};

int main()
 {
    class X x; //what is this? explain it
    class Y y; //what is this? explain it
    class Z z; //what is this? explain it    //error
    return 0;
  }
</code></pre>

<p>Edited: May i know the exact difference between "Class Z z" and "Z z".Because While 
compiling this program in 2 ways</p>

<pre><code>  class Z Z;   //here iam getting as Error: error: incomplete type is not allowed
  Z z; //error: identifier "Z" is undefined
</code></pre>

<p>Since iam asking the exact difference.</p>
