求解决！

 class Program
    {
        static void Main(string[] args)
        {
            int age;
           string y；
                        Console.WriteLine("请输入年龄:");
            age=Convert.ToInt32(Console.ReadLine());
            if (age >= 18)
            {
                Console.WriteLine("可以继续查看");
            } 
                
            }
           
            else if（age>=10&&age<18）
            {
                Console.WriteLine("您真的想继续吗？请输入yes或者no:");
                y = Console.ReadLine();
                           if (y == yes) { Console.WriteLine("请继续查看"); }
                else{ Console.WriteLine("不允许查看"); }
            }
               else  { Console.WriteLine("不允许产看");  
        }
    }
}
错误代码为：当前上下文中不存在名称yes