title: I need a Regular Expression allowing user to input numbers, plus, minus and parentheses
body: <p>I need a Regular Expression allowing user to input numbers, plus, minus and parentheses.</p>
  
  <p>User can only input:</p>
  
  <ul>
  <li>At most one open parenthesis '('. </li>
  <li>At most one close parenthesis ')'.</li>
  <li>At most one plus '+'</li>
  <li>As many minus '-' but not after each other.</li>
  <li>Exactly 11 numbers.</li>
  </ul>
  
  <p>Here are valid inputs:</p>
  
  <pre><code>(0)+12-3-4-56-7890
  +)0(12345-678-90
  +01234567890
  +(01234567890)
  01234567890
  -01-234+5678-90
  (01234567890)
  )01234567890(
  </code></pre>
  
  <p>And following are not valid:</p>
  
  <pre><code>0123456--7890
  0((1234567890
  01234567890))
  ++01234567890
  123456
  ++123456789
  </code></pre>
  
  <p>I'm using C# for programming and if it helps order of open and close parentheses can become mandatory too. so <code>)01234567890(</code> will not be valid.</p>
  
  <p>Thanks in advance</p>