for (int i = 1; i <= Convert.ToInt32(input); i++)
{
    panel1.Controls.Add(new TextBox()
    {
        Name = i.ToString(),
        Location = new Point(54, yTextBox_n = yTextBox_n + 35),
        Font = new Font("Times New Roman", 14.25f)
    });

    panel1.Controls.Add(new Label()
    {
        Name = i.ToString(),
        Location = new Point(8, yLabel_n = yLabel_n + 35),
        Text = "n" + i,
        Font = new Font("Times New Roman", 14.25f, FontStyle.Italic)
    });
}

class Class_Algorithm
{
    int[,] Matrix;
    int L;
    int N;

    public Class_Algorithm(int[,] matrix, int l, int n)
    {
        Matrix = matrix;
        L = l;
        N = n;
    }

    public void Algorithm()
    {
        int k = 1;
        int q = 1;

        for (int d = 0; d < L; d++)
        {
            int m = 1;
            int z = 1;
            int[] r = new int[N];

            for(int i = 0; i < N; i++)
            {
                for(int j = 0; j < N; j++)
                {
                    r[i] += Matrix[i, j];
                }
            }
        }
    }
}

this.Controls.Find("ControlName", false);

private Dictionary<int, TextBox> dynamicTextboxes = new Dictionary<int, TextBox>();

private string TextByIndex(int index)
{
  string result = "";
  if (dynamicTextboxes.ContainsKey(index))
    result = dynamicTextboxes[index].Text;
  return result;
}


dynamicTextboxes.Clear();
for (int i = 1; i <= Convert.ToInt32(input); i++)
{
    TextBox box = new TextBox()
    {
        Name = "textbox_" + i.ToString(),
        Location = new Point(54, yTextBox_n = yTextBox_n + 35),
        Font = new Font("Times New Roman", 14.25f)
    };
    dynamicTextboxes[i] = box;
    panel1.Controls.Add(box);

    panel1.Controls.Add(new Label()
    {
        Name = "label_" + i.ToString(),
        Location = new Point(8, yLabel_n = yLabel_n + 35),
        Text = "n" + i,
        Font = new Font("Times New Roman", 14.25f, FontStyle.Italic)
    });
}