Creating multiple objects in loop

Question

This is my first time, so... be gentle ;) Welcome community!

Here's my problem. I have to create multiple objects inside a loop. But I don't know how to do it. Already tried doing it this way:

List<myClass> ObjectList = new List<MyClass>();

and then :

ObjectList.Add(new MyClass(a,b));

Class is with descriptor and params "a" and "b" are set.

So, I'm looking for this :

class myClass
{
    int a;
    int b;
    public MyClass(int A, int B)
    {
        a=A; 
        b=B;
    }

    class Main()
    {
        Random r=new Random();
        MyClass a1 = new MyClass(r.Next(0,11));
        MyClass a2 = new MyClass(r.Next(0,11));
        MyClass a3 = new MyClass(r.Next(0,11));
        MyClass a4 = new MyClass(r.Next(0,11));
        MyClass a5 = new MyClass(r.Next(0,11));
        MyClass a6 = new MyClass(r.Next(0,11));
    }
}

And I have to find a way to create these objects in the loop, cause I cannot know how many of these will be, as I'm reading a matrix from a file.

So what's the problem, why can't you use a loop? Show your effort. Show how your file looks like. — Tim Schmelter
– Tim Schmelter, Commented Apr 11, 2016 at 10:55
If you don't know how many objects there are, you can use a while(!endOfFile) { } and create each object and add it to the list — Rob
– Rob ♦, Commented Apr 11, 2016 at 10:55
You can use your code inside of a loop : ObjectList.Add(new MyClass(r.Next(0,11), r.Next(0,11)));. As it is shown it's difficult to understand your problem and how we can help to solve it. — Fabjan
– Fabjan, Commented Apr 11, 2016 at 10:57

Matthew Watson · Accepted Answer · 2016-04-11 11:08:11Z

There is a common solution to the situation where you want to initialise something by repeatedly attempting to acquire an item from a source until the source runs out.

This is called a "loop-and-a-half" construct (and it's a proper "structured" construct, since it is a loop with a single exit).

The general approach goes like this:

while (true)
{
     attempt to obtain next item;

     if (no more items available)
         break loop;

     add item to collection;
}

A general implementation in C# might look like this:

class MyClass
{
}

class MyInitData
{
}

static class Program
{
    static void Main(string[] args)
    {
        var list = new List<MyClass>();

        while (true)
        {
            var initData = GetNextItem(); // Returns null when no more items are available.

            if (initData == null) // No more items available.
                break;

            list.Add(CreateMyClassFromInitData(initData));
        }
    }

    static MyInitData GetNextItem() // Returns null when no more items are available.
    {
        // Code to return next item. Implementation omitted here.
        return null;
    }

    static MyClass CreateMyClassFromInitData(MyInitData initData)
    {
        // Create a new MyClass from initData. Implementation omitted here.
        return new MyClass();
    }
}

As another - simpler - example, here's how you might go about reading number strings from a text file and converting them into a list of ints, using a loop-and-a-half:

var list = new List<int>();

using (var reader = File.OpenText("MyFileName.txt"))
{
    while (true)
    {
        string line = reader.ReadLine();

        if (line == null)
            break;

        list.Add(int.Parse(line));
    }
}

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