Need help using REF and Arrays, and Methods

问题

Ok, I'm doing my lab from C# class which involve using ref parameters, arrays, and methods. There is a few problems which I encounter while doing this and I'm begging for help. So.. First I modified problem into simplest chunks to help me explain which problems I have. Here is a piece of simplified code:

using System;

public class Repository 
{
    string[] titles;

    static void Main(string[] args)
    {
        string title;

        Console.Write("Title of book: ");
        title = Console.ReadLine();

        getBookInfo(ref title);
    }

    static void getBookInfo(ref string title)
    {
        titles[0] = title;
    }

    static void displayBooks(string[] titles)
    {
        Console.WriteLine("{0}", titles[0]);
    }
}

Now, as u will try to compile code, you notice that can not be compiled because error say "An object reference is required to access non-static member 'Repository.titles'". The problem is that the format of 3 methods must b exactly as posted as told in the assignment. Now, how can I avoid this problem while keeping this template in place?

Other question, how would I display content of method displayBooks in main? (I haven't got this far because of problems).

Regards, and please help!

----------------------- THANK YOU FOR HELP !!! ---------

回答1:

Firstly, you don't need to use ref unless you want to alter the value of title as it exists within Main(). The following code demonstrates the concept:

static void Main(string[] args)
{
    string a = "Are you going to try and change this?";
    string b = "Are you going to try and change this?";

    UsesRefParameter(ref a);
    DoesntUseRefParameter(b);
    Console.WriteLine(a); // I changed the value!
    Console.WriteLine(b); // Are you going to try and change this?
}

static void UsesRefParameter(ref string value)
{
    value = "I changed the value!";
}

static void DoesntUseRefParameter(string value)
{
    value = "I changed the value!";
}

An array needs to be created before you can use it. So here is your code that has been corrected:

static string[] titles;

static void Main(string[] args)
{
    string title;
    titles = new string[1]; // We can hold one value.

    Console.Write("Title of book: ");
    title = Console.ReadLine();

    getBookInfo(title);
}

static void getBookInfo(string title)
{
    titles[0] = title;
}

To display your books you could try the following method:

static void displayBooks(string[] titles)
{
    // Go over each value.
    foreach (string title in titles)
    {
        // And write it out.
        Console.WriteLine(title);
    }
}
// In Main()
displayBooks(titles);

回答2:

For your first question, make titles static:

private static string[] titles;

回答3:

Ok first of all you're trying to assign title to index 0 of an array called titles which has not been initialized yet. Essentially it is a null array at the time you are trying to assign a value to it.

The quick way to satisfy this problem is to modify your code like this:

private static string[] titles;

    static void Main(string[] args)
    {

        string title;

        Console.Write("Title of book: ");
        title = Console.ReadLine();

        getBookInfo(ref title);
        displayBooks(titles);
    }

    static void getBookInfo(ref string title)
    {
        //titles[0] = title;
        titles = new string[] {title};
    }

    static void displayBooks(string[] titles)
    {
        Console.WriteLine("{0}", titles[0]);
    }

If you want to assign more books to this array and print them out you need to initialize the array with the size. I would just use a List<string> which can be added to without defining the intial size.

To set the titles array to a size simply do this: static string[] titles = new string[50];

Going over what this program intends to do, there is more logic that needs to be added. Such as a counter variable to add a title to the next index in the titles array.

来源：https://stackoverflow.com/questions/7313320/need-help-using-ref-and-arrays-and-methods

标签

arrays

methods

ref