title: How to check the sub string is exists or not in main string
body: <p>Is there any way to check the sub string is exists in main string or not. If exits, no need any another action. If not exists, I want to add some another string to main string. </p>
  
  <p>For an example:</p>
  
  <pre><code>$a = 'Hello world';
  $b = 'Hello';
  </code></pre>
  
  <p>I want to check the <code>$b</code> is exists in <code>$a</code> or not. If exists, i am sending that variable to database. If not exists, I want to use <code>str_replace('Hello', $b.'World', $b)</code>.</p>