title: int value under 10 convert to string two digit number
body: <pre><code>string strI;   
  
  for (int i = 1; i &lt; 100; i++)
      strI = i.ToString();
  </code></pre>
  
  <p>in here,  if <code>i = 1</code> then <code>ToString</code> yields <code>"1"</code></p>
  
  <p>But I want to get  <code>"01"</code> or <code>"001"</code></p>
  
  <p>It looks quite easy, but there's only article about </p>
  
  <pre><code>datetime.ToString("yyyy-MM-dd")`
  </code></pre>