Using recursion to sum numbers

Question

I have just been studying the concept of recursion and I thought that I would try a simple example. In the following code, I am attempting to take the numbers: 1, 2, 3, 4, 5, an

Answer 1

To begin at the end, a recursive Sum method looks like this:

    // version 3

    public static int Sum(int startRange, int endRange)
    {
        if (endRange > startRange)
        {
            return endRange + Sum(startRange, endRange - 1);

        }

        if (endRange < startRange)
        {
            return startRange + Sum(endRange, startRange - 1);

        }

        return endRange; 

    }

Hardcoding the startRange to be 0 gives us:

    // version 2

    public static int Sum(int range)
    {
        if (range > 0)
        {
            return range + Sum(0, range - 1);

        }

        if (range < 0)
        {
            return Sum(range, -1);

        }

        return range;

    }

...and if you want to limit the method to positive numbers only, there's no need for a sign:

    // version 1

    public static unsigned int Sum(unsigned int range)
    {
        if (range > 0)
        {
            return range + Sum(0, range - 1);

        }

        return range;

    }

I hope this helps give more of an insight into summing number ranges via recursion.