public insert() {
    Console.Write("请输入姓名：");
    String name = Console.ReadLine();
    Console.Write("请输入年龄：");
    String age = Console.ReadLine();
    Console.Write("请输入地址：");
    String add = Console.ReadLine();

    SqlConnection conn = new SqlConnection(@"server=.;database=mydb;uid=sa;pwd=sa");

    //第一种占位符的使用方式
    SqlCommand cmd = conn.CreateCommand();
    cmd.CommandText = "insert into login values(@username,@userage,@useradd)";
    cmd.Parameters.AddWithValue("@username", name);
    cmd.Parameters.AddWithValue("@userage", age);
    cmd.Parameters.AddWithValue("@useradd", add);

    //第二种占位符的使用方式
    String sql = string.Format("insert into login values('{0}',{1},'{2}')", name, age, add);
    SqlCommand cmd = new SqlCommand(sql, conn);

    try {
            conn.Open();
            int i = cmd.ExecuteNonQuery();
            if (i > 0) {
                    Console.WriteLine("插入数据成功");
            }
            cmd.Dispose();
            conn.Close();
    } finally {
            conn.Close();
    }
}