title: Replace the digits in the string with #
body: <p>Consider a string that will have digits in that, we need to remove all the characters which are not digits and replace the digits with #</p>
  
  <p>Ex 1: </p>
  
  <pre><code>A = 234                
        Output: ###
  </code></pre>
  
  <p>Ex 2: </p>
  
  <pre><code>A = a2b3c4             
        Output: ###
  </code></pre>
  
  <p>Ex 3: </p>
  
  <pre><code>A = abc                
        Output:   (empty string)
  </code></pre>
  
  <p>Ex 4: </p>
  
  <pre><code>A = #2a$#b%c%561#      
        Output: ####
  </code></pre>