RecursiveLambda.cs

using System;
class Program
{
    static void Main()
    {
        int num = 10;
        Console.WriteLine(AddUpToLoop(num));
        Console.WriteLine(AddUpToRecursive(num, 0));
        Func<int, int, int> AddUpToLambda = null;
        AddUpToLambda = (num, sum) => { return num == 0 ? sum : AddUpToLambda(--num, sum + num + 1); };
        Console.WriteLine(AddUpToLambda(num, 0));
    }
    static int AddUpToLoop(int num)
    {
        int sum = 0;
        for (int i = 1; i <= num; i++)
        {
            sum += i;
        }
        return sum;
    }
    static int AddUpToRecursive(int num, int sum)
    {
        if (num == 0) return sum;
        sum += num;
        num--;
        return AddUpToRecursive(num, sum);
    }
}