title: using memset() in double type array
body: <p>I want to set all the index value to <code>-1</code> in a double array.<br>
  Here is my code :</p>
  
  <pre><code>double dp[505];
  memset(dp,-1,sizeof(dp));
  cout&lt;&lt;dp[0]&lt;&lt;"\n";
  </code></pre>
  
  <p>But it is showing <code>nan</code> when i try to print its value.  </p>
  
  <p>What does <code>nan</code> mean?
  Is it possible to use <code>memset()</code> in double array?</p>