class WriteTextFile
    {
        static void Main()
        {
            //如果文件不存在，則創建；存在則覆蓋
            //該方法寫入字符數組換行顯示
            string[] lines = { "first line", "second line", "third line","第四行" };
            System.IO.File.WriteAllLines(@"C:/testDir/test.txt", lines, Encoding.UTF8);
            //如果文件不存在，則創建；存在則覆蓋
            string strTest = "該例子測試一個字符串寫入文本文件。";
            System.IO.File.WriteAllText(@"C:/testDir/test1.txt", strTest, Encoding.UTF8);
            //在將文本寫入文件前，處理文本行
            //StreamWriter一個參數默認覆蓋
            //StreamWriter第二個參數為false覆蓋現有文件，為true則把文本追加到文件末尾
            using (System.IO.StreamWriter file = new System.IO.StreamWriter(@"C:/testDir/test2.txt",true))
            {
                foreach (string line in lines)
                {
                    if (!line.Contains("second"))
                    {
                        file.Write(line);//直接追加文件末尾，不換行
                        file.WriteLine(line);// 直接追加文件末尾，換行  
                    }
                }
            }
        }
    }

class ReadTextFile
    {
        static void Main()
        {
            //直接讀取出字符串
            string text = System.IO.File.ReadAllText(@"C:/testDir/test1.txt");
            Console.WriteLine(text);
            //按行讀取為字符串數組
            string[] lines = System.IO.File.ReadAllLines(@"C:/testDir/test.txt");
            foreach (string line in lines)
            {
                Console.WriteLine(line);
            }
            //從頭到尾以流的方式讀出文本文件
            //該方法會一行一行讀出文本
            using (System.IO.StreamReader sr = new System.IO.StreamReader(@"C:/testDir/test.txt"))
            {
                string str;
                while ((str = sr.ReadLine()) != null)
                {
                    Console.WriteLine(str);
                }
            }
            Console.Read();
        }
    }