Question

I have a textarea where user can create a dynamic formulas using dropdown lists(for operators, variables etc) like this:

basic / workingDays * attendingDays

where values of basic, workingDays, attendingDays are saved in database. I want to map these variable from database during runtime. How can I do this.

Answer 1

NCalc is a very powerful framework that you could try. They let you define dynamic parameters which sounds like exactly what you need. You can do something like this:

var e = new Expression("basic / workingDays * attendingDays);

//Set up a custom delegate so NCalc will ask you for a parameter's value
//   when it first comes across a variable
e.EvaluateParameter += delegate(string name, ParameterArgs args)
{
   if (name == "basic")
       args.Result = GetBasicValueFromSomeWhere();
   else if (/* etc. */)
   {
       //....
   }

   //Or if the names match up you might be able to something like:
   args.Result = dataRow[name];
};

var result =  e.Evaluate();

There are also some related questions out there such as this one and this one that give some other options.