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 n = 6;

        var cResult = 1;

        while (n > 1)

        {

            cResult = cResult * n;

            n--;

        }

        Console.WriteLine(cResult);

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

        var nArgument = Expression.Parameter(typeof(int), "n");

        var result = Expression.Variable(typeof(int), "result");

​

        // Creating a label that represents the return value

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

​

        var initializeResult = Expression.Assign(result, Expression.Constant(1));

​

        // This is the inner block that performs the multiplication,

        // and decrements the value of 'n'

        var ifTrueBlock = Expression.Block(

            Expression.Assign(result,

                Expression.Multiply(result, nArgument)),

            Expression.PostDecrementAssign(nArgument)

        );

​

        var ifThenElseExpr = Expression.IfThenElse(

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

            ifTrueBlock,

            Expression.Break(label, result)

        );

​

        // Creating a method body.

        BlockExpression body = Expression.Block(

            new[] { result },

            initializeResult,

            Expression.Loop(ifThenElseExpr, label)

        );

​

        // Compile and run an expression tree.

        var factorial = Expression.Lambda<Func<int, int>>(body, nArgument).Compile();

​

        Console.WriteLine(factorial(6));

    }

}