title: Adding nCr Function to DDMathParser (with variable parameters)
body: <p>I'm struggling to add a new function (nCr) to DDMathParser. I've tried to follow these instructions by the author of DDMathParser:</p>
  
  <p><a href="https://stackoverflow.com/a/15599814/2521277">https://stackoverflow.com/a/15599814/2521277</a></p>
  
  <p>My problem: I can't manage to combine DDExpressions to a complex expression with variables...</p>
  
  <p>Can you help me to add the function nCr (<a href="http://en.wikipedia.org/wiki/Binomial_coefficient#Factorial_formula" rel="nofollow noreferrer">http://en.wikipedia.org/wiki/Binomial_coefficient#Factorial_formula</a>)</p>
  
  <p>Thank you!</p>