Problem with output of mergesort algorithm

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C#

algorithm

This code gives output but it has one problem that is when user write 5,6 in textbox1 and 7,8 in textbox3 it gives output 5,6.
I know the problem is that when the elements of an array ends,it doesnt print the rest elements of other array, I commented on line of problem.

*I used textbox1 and textbox3 for getting the elements of the arrays that user wants to merge

private void button3_Click(object sender, EventArgs e)
{

    string[] source = textBox1.Text.Split(',');
    string[] source1 = textBox3.Text.Split(',');
    int[] nums2 = new int[8];
    int[] nums = new int[source.Length];
    for (int i = 0; i < source.Length; i++)
    {
        nums[i] = Convert.ToInt32(source[i]);
    }
    int[] nums1 = new int[source1.Length];
    for (int j = 0; j < source1.Length; j++)
    {
        nums1[j] = Convert.ToInt32(source1[j]);
    }
    int x = 0;
    int y = 0;
    int z = 0;
    while (x < nums.Length && y < nums1.Length)
    {
        if (nums[x] < nums1[y])
        {
            nums2[z] = nums[x];
            x++;
        }
        else
        {
            nums2[z] = nums1[y];
            y++;
        }
        z++;
    }////----->>it works untill here
    while (x > nums.Length)///this mean when the elements of nums end,out the rest of the elements in other textbox but it doesnt do anything,whats the problem ?
    {
        if (y <= nums1.Length)
        {
            nums2[z] = nums1[y];
            z++;
            y++;
        }
    }
    while (y > nums1.Length)
    {
        if (x <= nums.Length)
        {
            nums2[z] = nums[x];
            z++;
            x++;
        }
    }
        string merge = "";
        foreach (var n in nums2)
            merge += n.ToString() + ",";
        textBox4.Text = merge;

    }