title: Cannot implicitly convert type 'ulong' to 'bool'
body: <p>I get this error: </p>
  
  <blockquote>
    <p>Cannot implicitly convert type 'ulong' to 'bool'</p>
  </blockquote>
  
  <p>in here (u*u) <code>for (ulong u = 2; u * u; u++)</code></p>
  
  <p>chunk of code below.</p>
  
  <pre><code>static bool IsPrime(ulong Num)
  {
       if (Num &lt; 2) return false;
       else if (Num &lt; 4) return true;
       else if (Num % 2 == 0) return false;
       for (ulong u = 2; u * u; u++)
           if (Num % u == 0) return false;
       return true;
  }
  </code></pre>