using System;

using System.Linq.Expressions;

using System.Collections;

using System.Collections.Generic;

using System.Linq;

public class Program

{

    public static void Main()

    {

        Console.WriteLine("****************** C# Equivalent Output **************************\n\n");

        int cValue = 6;

​

        var cResult = 1;

        while (cValue > 1)

        {

            cResult = cResult * cValue;

            cValue--;

        }

        Console.WriteLine(cResult);

​

        Console.WriteLine("\n\n***************** Expression Tree Output **************************\n\n");

        ParameterExpression value = Expression.Parameter(typeof(int), "value");

​

        // Creating an expression to hold a local variable. 

        ParameterExpression result = Expression.Parameter(typeof(int), "result");

​

        // Creating a label to jump to from a loop.

        LabelTarget label = Expression.Label(typeof(int));

        ConditionalExpression ifThenElseExpr = Expression.IfThenElse(

            Expression.GreaterThan(value, Expression.Constant(1)),

            Expression.MultiplyAssign(result,

                Expression.PostDecrementAssign(value)),

            Expression.Break(label, result)

            );

​

        LoopExpression loop = Expression.Loop(ifThenElseExpr, label);

​

        // Creating a method body.

        BlockExpression block = Expression.Block(

            new[] { result },

            Expression.Assign(result, Expression.Constant(1)),

            loop

            );

​

        // Compile and run an expression tree.

        var factorial = Expression.Lambda<Func<int, int>>(block, value).Compile();

​

        Console.WriteLine(factorial(6));

    }

}