E：\a.txt文本内容

  ab

  cd

  ef

假设删除第二行

运行后的结果E：\a.txt文本内容

   ab

   ef

private void button1_Click(object sender, EventArgs e)         {                    string t="";             string[] a = File.ReadAllLines(@"E:\a.txt",  System.Text.Encoding.Default);//获取文本中每一行数据存在数组中             for (int i = 1; i < 2; i++)   // 利用算法进行覆盖的操作             {                 t = a[i];                 a[i] = a[i + 1];                 a[i + 1] = t;             }             StreamWriter sw = new StreamWriter(@"E:\a.txt", false, System.Text.Encoding.Default);             for (int j = 0; j < 2; j++)            {             sw.Write(a[j]);             sw.WriteLine();            }            sw.Flush();            sw.Close();         }