C＃如何在方法中使用部分填充的数组？

Question

My instructor wants us to create an array of 10 elements and then fill it with random numbers using console input and then multiply all the numbers together to get the product. I can't figure out how to pass the array to a method and then successfully get the product. Do I use a for loop? I don't think I can use a foreach loop because it could be partially filled. How do I even pass the array to the method in the first place?

Here's what I have so far to store the values in the array.

for (int i = 0; i < SIZE; i++)
{

    bool valid = false;
    do
    {
         Write("Enter an integer value or 0 to stop ");
         string input = ReadLine();
         valid = int.TryParse(input, out userInput);
    } while (!valid);

    if (userInput == 0)
    {
         break;
    }
    array[i] = userInput;
}

product = p.ArrayProduct(array.Length);

Answer 1

The method for multiplying is as below:

public int ArrayProduct(int[] array)
{
   int p = 1;
   for(int i = 0; i < array.Length; i++)
   {
       p *= array[i];
   }
   return p;
}

You can multiply in foreach loop as well:

public int ArrayProduct(int[] array)
{
   int p = 1;
   foreach(int element in array)
   {
       p *= element;
   }
   return p;
}

Or you can use Array class like below:

public int ArrayProduct(int[] array)
{
    int p = 1;
    Array.ForEach(array, el =>
    {
        p *= el;
    });
    return p;
}

There is another extension method for arrays called, gues how! ForEach

public int ArrayProduct(int[] array)
{
    int p = 1;
    array.ForEach(element =>
    {
        p *= element;
    });
    return p;
}

Then you call it after you have the data as below:

int product = ArrayProduct(array);
Console.WriteLine(product);

There is another way as @Peter A. Schneider said by using Linq according this question here

public int ArrayProduct(int[] array)
{
    return array.Aggregate(1, (acc, val) => acc * val);
}

better in c# 6 and above:

public int ArrayProduct(int[] array) => array.Aggregate(1, (acc, val) => acc * val);

If you have problem with getting the data please let me know!

Answer 2

You can call a method by reference. You should use from out and ref key word: https://msdn.microsoft.com/en-us/library/t3c3bfhx.aspx

Answer 3

Here's an example of tracking the number of entries in a separate variable and passing that to the processing function along with the array:

static void Main(string[] args)
{
    int SIZE = 10;
    int numEntries = 0;
    int[] array = new int[SIZE];

    Console.WriteLine("Enter up to " + SIZE.ToString() + " integer(s).");

    string input;
    int userInput;
    for (int i = 0; i < array.Length; i++)
    {
        bool valid = false;
        do
        {
            Console.Write("Enter integer #" + (i+1).ToString() + " or 0 to stop: ");
            input = Console.ReadLine();
            valid = int.TryParse(input, out userInput);
            if (!valid)
            {
                Console.WriteLine("Invalid entry!");
            }
        } while (!valid);

        if (userInput == 0)
        {
            break;
        }

        numEntries++;
        array[i] = userInput;
    }

    if (numEntries > 0)
    {
        int product = ArrayProduct(array, numEntries);
        Console.WriteLine("The product is " + product.ToString("n0") + ".");
    }
    else
    {
        Console.WriteLine("No entries were made!");
    }

    Console.Write("Press [Enter] to quit.");
    Console.ReadLine();
}

private static int ArrayProduct(int[] arr, int length)
{
    int product = 1;
    if (length <= arr.Length)
    {
        for(int i = 0; i < length; i++)
        {
            product = product * arr[i];
        }
    }
    return product;
}