[真的很紧急]大家帮忙，怎么让textbox根据自动调整高度

[真的很紧急]大家帮忙，如何让textbox根据自动调整高度？
代码如下：
  private void textBox1_TextChanged(object sender, EventArgs e)
  {
  TextBox textBox1 = (TextBox)sender;
  Graphics grp = textBox1.CreateGraphics();
  SizeF textsize = grp.MeasureString("啊", textBox1.Font);
  double length = 0;
  char[] c = textBox1.Text.ToCharArray();
  int i = textBox1.Text.Split('\r').Length + 1;
  Regex r = new Regex("[^\x00-\xff]");
  foreach (char cc in c)
  {
  Match m = r.Match(c.ToString());
  if (m.Success)
  {
  ++length;
  }
  else
  {
  length += 0.5;
  }
  }
   
  int width = (int)textsize.Width * 10;
  int height = (int)textsize.Height * (int)(length / 10 + i);
  textBox1.Size = new Size(width, height);
  grp.Dispose();
  }

这段代码测试算是成功，其中数字“10”是指定每行最多可输入10个字（为防止控件大小溢出），那么如何根据内容而自动调整高度？
这段代码测试时不稳定……请高手帮忙下。我这项目下礼拜4急用！！学校要用的……

[解决办法]
根据内容自动调整滚动条的代码，照着改改应该能行

C# code

private void textBox5_TextChanged(object sender, System.EventArgs e)        {            TextBox tb=(TextBox) sender;            ShowScrollBar(tb);        }private  void ShowScrollBar(TextBox tb)        {            //TextBox 当超出界面时显示垂直滚动条            if(tb.Lines.Length>tb.Height/tb.Font.Height)            {                tb.ScrollBars=System.Windows.Forms.ScrollBars.Vertical;            }            else            {                tb.ScrollBars=System.Windows.Forms.ScrollBars.None;            }        }
[解决办法]
        private void textBox1_TextChanged(object sender, EventArgs e)
       {
           int t = getline();
           Graphics g = this.textBox1.CreateGraphics();
           SizeF ss = g.MeasureString("测试", this.textBox1.Font);
           int h = (int)ss.Height + 3; 
           if (t <= 5)
           {
               this.textBox1.Height = t * h;
               this.textBox1.ScrollBars = ScrollBars.None;
           }
           else
           {
               this.textBox1.Height = 5 * h;
               this.textBox1.ScrollBars = ScrollBars.Vertical;
           }
       }
       private int getline()
       {
           Graphics g = this.textBox1.CreateGraphics();
           int lines=0;
           foreach(string s in this.textBox1.Lines)
           {
               SizeF ss=g.MeasureString(s,this.textBox1.Font);
               lines += ((int)ss.Width / this.textBox1.Width + 1);
              
           }

           return lines;
    
       }