Question

I am trying to Quicksort 10 random numbers within an listbox. But i cant use the method on my random iar, can anyone give me some advice.

Code behind button:

         private void btnSort_Click(object sender, EventArgs e)
    {
        Random r = new Random();
        int n = 10;
        int[] iar = new int[n];
        for (int i = 0; i < iar.Length; i++)
        {
            iar[i] = r.Next(0, 20);
            lb1.Items.Add(iar[i]);

        //here is the error i want to fill lb2 with the quicksorted array 
        // using the quicksort method

            Quicksort(iar, 0, iar.Length - 1);
        }
        for (int i = 0; i < iar.Length; i++)
        {
            lb2.Items.Add(iar[i]);
        }
    }

Quicksort method

 public static void Quicksort(IComparable[] elements, int left, int right)
    {
        int i = left, j = right;
        IComparable pivot = elements[(left + right) / 2];

        while (i <= j)
        {
            while (elements[i].CompareTo(pivot) < 0)
            {
                i++;
            }
            while (elements[j].CompareTo(pivot) > 0)
            {
                j--;
            } 
            if (i <= j)
            {
                // Swap
                IComparable tmp = elements[i];
                elements[i] = elements[j];
                elements[j] = tmp;

                i++;
                j--;
            }
        }
        // Recursive calls
        if (left < j)
        {
            Quicksort(elements, left, j);
        }
        if (i < right)
        {
            Quicksort(elements, i, right);
        }
    }

}

ERRORS:

Error 2 Argument 1: cannot convert from ‘int[]’ to ‘System.IComparable[]’
Error 1 The best overloaded method match for ‘Quicksort.FrmQuicksort.Quicksort(System.IComparable[], int, int)’ has some invalid arguments

Thanxs for looking:)

Answer 1

In the given context there is no real need to specify IComparable rather than int because you are only ever using integers. You’re also calling QuickSort as each number is generated when it will work best if you run the QuickSort algorithm on the already generated list so move the statement outside the loop. Also bare in mind that there are better sorting algorithms for sorting tiny amounts of data like this.

Click Event Handler:

private void btnSort_Click(object sender, EventArgs e)
{
    Random r = new Random();
    int n = 10;
    int[] iar = new int[n];

    //Generate random numbers and store them in the Unsorted ListBox
    for (int i = 0; i < iar.Length; i++)
    {
        iar[i] = r.Next(0, 20);
        lb1.Items.Add(iar[i]);
    }

    //Sort the random numbers array
    Quicksort(iar, 0, iar.Length - 1);

    //Now the array is sorted put it in the Sorted Listbox
    for (int i = 0; i < iar.Length; i++)
    {
        lb2.Items.Add(iar[i]);
    }
}

QuickSort Function

//Take an array of integers not an array of IComparable
public static void Quicksort(int[] elements, int left, int right)
{
    int i = left;
    int j = right;

    int pivot = elements[(left + right) / 2];

    while (i <= j)
    {
        while (elements[i].CompareTo(pivot) < 0)
        {
            i++;
        }
        while (elements[j].CompareTo(pivot) > 0)
        {
            j--;
        }


        if (i <= j)
        {
            // Swap
            int tmp = elements[i];
            elements[i] = elements[j];
            elements[j] = tmp;

            i++;
            j--;
        }
    }
    // Recursive calls
    if (left < j)
    {
        Quicksort(elements, left, j);
    }
    if (i < right)
    {
        Quicksort(elements, i, right);
    }
}