Using recursion to calculate sum of only positive elements in array

An array gets filled up with random elements (negative and positive). Now I want to calculate the sum of ONLY the positive elements.

I开发者_运维问答terative there is no problem, but in the recursion version I can only get the sum of both negative and positive.

How can I "check" in the recursive version that it only sums up the positive elements?

Iterative version:

public int IterSomPosElem(int[] tabel, int n)
{
    n = 0;

    for (int i = 0; i < tabel.Length; i++)
    {
        if (tabel[i] >= 0)
        {
            n += tabel[i];
        }
    }

    return n;
}

Recursive version at the moment (sums up all the elements instead of only the positive):

public int RecuSomPosElem(int[] tabel, int n)
{
    if(n == 1)
        return tabel[0]; //stopCriterium
    else
    {
        return (tabel[n - 1] + RecuSomPosElem(tabel, n - 1)); // how to check, so it only sums up the postive elements and "ignores" the negative elements.
    }
}

Is this homework? Why do you need to do this with a recursive function?

In the real world, it would be some simple LINQ

int positiveSum = tabel.Where(i => i > 0).Sum();

How about

int foo[] = new [] {1, -9, 10, 8, -16, ...};
int sumOfPostiveInts = foo.Sum(x => x < 0 ? 0 : x);

or...foo.Where(x => x > 0).Sum();

Something like?

public int RecuSomPosElem(int[] tabel, int n) 
    { 
        if(n == 1) 
            return tabel[0]; //stopCriterium 
        else 
        { 
            var valueToSum = tabel[n - 1] > 0 ? tabel[n - 1] : 0;
            return (valueToSum + RecuSomPosElem(tabel, n - 1)); 
        } 

    } 

public int RecuSomPosElem(int[] tabel, int n)
{
    if(n == 1)
        return tabel[0]; //stopCriterium
    else
    {

        if (tabel[n - 1] > 0)
            return (tabel[n - 1] + RecuSomPosElem(tabel, n - 1)); 
        else
            return RecuSomPosElem(tabel, n - 1));
    }

}

You're so close! Using your algorithm, but just adding a check to see if the current value in table is negative or not. If it is negative move on to the next array item:

    private static int RecuSomPosElem(int[] tabel, int n)
    {
        int i = n - 1;
        while (tabel[i] < 0 && i > 0)
            i--;
        if (i == 0)
        {
            return 0; //stopCriterium 
        }
        else
        {
            return (tabel[i] + RecuSomPosElem(tabel, i));
        }
    } 

Use this:

   public int Rsum(int[] data, int currentIndex, int LastIndex)
        {
            if(currentIndex < LastIndex)
            {
                if (data[currentIndex] > 0)
                {
                    return (data[currentIndex] + Rsum(data, ++currentIndex, LastIndex));
                }
                else
                {
                    return Rsum(data, ++currentIndex, LastIndex);
                }
            }
            return 0;
        }

See if it solves:

public int sumPositiveNumbersR(int[] v, int n){
int sum;
if(n < 0) return 0; //stopCriterium
else{
    if(v[n] > 0){
        sum = v[n] + sumPositiveNumbersR(v, n-1); //scrolls the vector and sum
        return sum;
    }else
        return sumPositiveNumbersR(v, n-1); //scrolls the vector
}