title: why we write #include<iostream> and #include<conio.h> in visual studio
body: <p>In visual studio c++ consider the following code</p>
  
  <pre><code>#include&lt;iostream&gt;
  #include&lt;conio.h&gt;
  using namespace std;
  int main()
  {
      cout&lt;&lt;"Hello!";
      return 0;
      _getch();
  }
  </code></pre>
  
  <p>In the above code in the <code>#include&lt;iostream&gt;</code> header file we dont use the <strong>.h</strong> extension because it produces an error.But in the header file <code>#include&lt;conio.h&gt;</code> the <strong>.h</strong> extension is added.
  Why does it produces error in case of <code>#include&lt;iostream&gt;</code> and not in case of <code>#include&lt;conio.h&gt;</code>
  If we write only conio it produces an error.
  And one more question why we use <strong>#include"iostream"</strong> header file when <strong>cout</strong> and <strong>cin</strong> are already included in <strong>namespace std</strong></p>