public void StepImage(string direction, PictureBox c)
        {
            int include1 = 0;
            if (numb.Length == 1)
            {
                include1 = Convert.ToInt32(numb[0].ToString());
            }
            else
            {
                include1 = Convert.ToInt32(numb[0].ToString() + numb[1].ToString());
            }

            if (direction == "right")
            {
                if (include1 < theory.Count - 1)
                {
                    c.Image = theory[include1+1];
                    numb = include1.ToString();
                    leftbtn.Enabled = true;
                    if (include1 + 1 == theory.Count - 1)
                    {
                        rightbtn.Enabled = false;
                    }
                }
            }

            else
            {
                if (include1 > 0)
                {
                    c.Image = theory[include1 - 1];
                    numb = include1.ToString();
                    rightbtn.Enabled = true;
                    if (include1 - 1 == 0)
                    {
                        leftbtn.Enabled = false;
                    }
                }
            }
        }