Beginner : C# recursive function

Question

help for Recursive Function that prints the average of the elements of an integer list and the number of elements larger than the average. in c#

good, what I have so far, is giving System.Stackoverflowexception error.

public static Double MediaLista(Double[] v)
{
    int i = 0;
    Double soma = 0;
    if (i < v.Length)
    {
        for (int j = 0; j < v.Length; j++)
        {
            soma += v[j];
        }
        i++;
        return soma / MediaLista(v);
    }
    else return 0;

}

static void Main(string[] args)
{
    Double[] v = {1,2,3,3,5};
    Double resul =  MediaLista(v);

}

Edit : I increased the functionality of taking the numbers larger than the average in the Medialist method itself. In all my method was like this.

        public static double MediaLista(int[] v, int ultimo)
    {
        if (ultimo == 0)
        {

            return v[0];
        }
        else
        {

            int qtdNumero = ultimo + 1;
            double soma = v[ultimo] + (qtdNumero - 1) * MediaLista(v, ultimo - 1);
            if (qtdNumero == v.Length) {
                for (int i = 0; i < v.Length; i++)
                {
                    if (v[i] > (soma / qtdNumero))
                    {
                        Console.WriteLine($"o numero {v[i]}  é maior que a média");
                    }
                }
            }

            return soma / qtdNumero;


        }

    }

Answer 1

StackOverflowException occurs when there is a overflow Stack memory, usually caused by over nested functions.

In the case on the line return soma / MediaLista(v); you didn’t change the vector at all v, causing it to call the method again, and again, and again..... until causing this exception. :)

I believe what you’re trying to do is return soma / v.Length;

---

EDIT

There is another mistake, this time of logic.

On the line soma += v[i]; you are making loop with the j but adding the element i, which is always 0.

---

EDIT 2.0 - Recursive Edition :P

Apparently it’s okay. :)

public static void Main()
{
    int[] v = { 1, 2, 9, 10, 25, 0};
    double media = Media(v, v.Length - 1);
    Console.Write(media);
}

public static double Media(int[] v, int ultimo)
{
    if (ultimo == 0)
        return v[0];

    int qtdNumero = ultimo+1;       
    double soma = v[ultimo] + (qtdNumero-1) * Media(v, ultimo-1);

    return soma/qtdNumero;
}

Answer 2

So I was able to do the recursion by taking the for and using if and instead of incrementing I was decreasing to recursion to get 0 and exit the loop and give me the result:

EDIT: I added the part that takes which elements are larger than the average

    private void MetroButton1_Click(object sender, EventArgs e)
    {
        double[] v = { 1, 2, 3, 3, 5 };
        double resul = MediaLista(v, v.Length, 0);
        //Elementos da array maiores do que a média
        string maiorMedia = string.Empty;
        for (int i = v.GetLowerBound(0); i <= v.GetUpperBound(0); i++)
        {
            if (v[i] > resul)
            {
                maiorMedia += v[i] + ",";                    
            }
        }
        metroLabel3.Text = Convert.ToString(resul);
        metroLabel4.Text = maiorMedia;

    }
    //média dos elementos de uma lista de inteiros
    public double MediaLista(double[] v, int tamanho, double media)
    {
        if (tamanho > 0)
        {                
            media = v[tamanho - 1] + MediaLista(v, tamanho - 1, media);
            if (tamanho == v.Length)
            {
                return media / v.Length;
            }
            return media;
        }
        else
            return 0;
    }

EDIT2:

Just to play a little more the part that takes which elements of the array are larger than the average, I made another option in LINQ for those who want to understand this feature that is widely used in Entity Framework and other Orms

        string maiorQueMedia = string.Empty;
        var query =
            from num in v
            where num > resul
            select num;
        foreach (double num in query)
            maiorQueMedia += num + ",";