title: Find pattern and replace to another pattern string
body: <p>I tried to check if string contains some patterns string For example: '4+3+6**4'.</p>
  
  <p>I want replace the pattern <code>**</code> to <code>pow(x,y)</code>.</p>
  
  <p>so i want the string will be <code>4+3+pow(6,4)</code>.</p>
  
  <p>i want to know if there any way by 'Regex'.</p>
  
  <p>trt.</p>