title: How to find the last occurrence of a set of characters from a string
body: <p>I'm trying to find the last operator (<code>+</code>, <code>-</code>, <code>*</code> or <code>/</code>) in a string.</p>
  
  <p>I was trying to use the method <code>string.indexof('operator', i);</code>, but in this case I could only get the single type of <code>operator</code>. Is there any better solution for this?</p>
  
  <p>The value of <code>string</code> could, for example, be:</p>
  
  <p><code>1+1/2*3-4</code></p>
  
  <p>or </p>
  
  <p><code>1/2-3+4*7</code></p>
  
  <p>It means the last operator could be any of them.</p>