程序代码：

public class student : IEnumerable<string>
{
    private string no;
    private string name;
    private string sex;
    private string hobby;

    public student()
    {
        no = "20010";
        name = "baomi";
        sex = "male";
        hobby = "computer game";
    }

    public string this[string item]
    {
        get
        {
            switch (item)
            {
                case "no":
                    return no;
                case "name":
                    return name;
                case "sex":
                    return sex;
                case "hobby":
                    return hobby;
                default:
                    return "bad indexing";
            }
        }
    }

    public IEnumerator<string> GetEnumerator()
    {
        yield return "no";
        yield return "name";
        yield return "sex";
        yield return "hobby";
    }

    IEnumerator IEnumerable.GetEnumerator()
    {
        return (this as IEnumerable<string>).GetEnumerator();
    }
}