1、建立一个文本文件
public class FileClass
{
    public static void Main()
    {
    WriteToFile();
    }
    static void WriteToFile()
    {
    StreamWriter SW;
    SW=File.CreateText("c:\MyTextFile.txt");
    SW.WriteLine("God is greatest of them all");
    SW.WriteLine("This is second line");
    SW.Close();
    Console.WriteLine("File Created SucacessFully");
    }
}

2、读文件
public class FileClass
{
    public static void Main()
    {
    ReadFromFile("c:\MyTextFile.txt");
    }
    static void ReadFromFile(string filename)
    {
    StreamReader SR;
    string S;
    SR=File.OpenText(filename);
    S=SR.ReadLine();
    while(S!=null)
    {
    Console.WriteLine(S);
    S=SR.ReadLine();
    }
    SR.Close();
    }
}

3、追加操作

public class FileClass
{
    public static void Main()
    {
    AppendToFile();
    }
    static void AppendToFile()
    {
    StreamWriter SW;
    SW=File.AppendText("C:\MyTextFile.txt");
    SW.WriteLine("This Line Is Appended");
    SW.Close();
    Console.WriteLine("Text Appended Successfully");
    }
}