title: Validate mathematical expressions using regular expression?
body: <p>I want to validate mathematical expressions using regular expression. The mathematical expression can be this</p>
  
  <ol>
  <li><p>It can be blank means nothing is entered</p></li>
  <li><p>If specified it will always start with an operator <code>+</code> or <code>-</code> or <code>*</code> or <code>/</code> and will always be followed by a number that can have 
  any number of digits and the number can be decimal(contains <code>.</code> in between the numbers) or integer(no '.' symbol within the number).
  examples : <code>*0.9</code> , <code>+22.36</code> , <code>- 90</code> , <code>/ 0.36365</code> </p></li>
  <li><p>It can be then followed by what is mentioned in point 2 (above line).
  examples : <code>*0.9+5</code> , <code>+22.36*4/56.33</code> , <code>-90+87.25/22</code> , <code>/0.36365/4+2.33</code></p></li>
  </ol>
  
  <p>Please help me out.</p>