finding multiple ocurrences of a string
<p>How can I find multiple occurrences of a string within a string? 
And replace the found string with another string in all occurrences? 
Say, I have the string below:</p>

<pre><code>"A cat is going. It is black-white stripped."
</code></pre>

<p>I want to replace all occurrences of "is" with are.</p>
