title: Regular expression to validate sum of numerics
body: <p>I want to validate the user input,</p>
  
  <p>it should accept,</p>
  
  <pre><code>1+2
  1.2+56+3.5
  </code></pre>
  
  <p>it should not accept any alphabets, special characters other than . and +</p>
  
  <p>and mainly it should not accept ++ and .. </p>
  
  <p>please help me with regular expression.</p>