C#

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace PrintQueueDemo
{
    class PrintQueue
    {
        Node head;
        Node tail;

        /// <summary>
        /// add a document to the print queue
        /// </summary>
        /// <param name="strType">document type</param>
        /// <param name="strName">docunent name</param>
        public void Push(string strType, string strName)
        {
            if (head == null)
            {
                head = new Node(strType, strName);
                tail = head;
            }
            else
            {
                Node node = new Node(strType, strName);
                tail.setNext(node);
                tail = node;
            }
        }

        /// <summary>
        /// pop a document from the queue
        /// </summary>
        /// <returns>null if printqueue is empty, else document</returns>
        public Node.Document Pop()
        {
            if (head == null)
                return null;

            Node.Document doc = new Node.Document(head.document.Type, head.document.Name);
            head = head.nextnode;
            if (head == null)
                tail = null;
            return doc;
        }

        /// <summary>
        /// get the current content of the queue
        /// </summary>
        /// <returns>string with current content (line per entry)</returns>
        public string DisplayContents()
        {
            string content = "";
            Node node = head;
            if (node == null)
                return "PrintQueue is empty";

            content = node.document.Name + ": " + node.document.Type;
            while (node.nextnode != null)
            {
                node = node.nextnode;
                content += "\r\n" + node.document.Name + ": " + node.document.Type;
            }
            return content;
        }

        public class Node
        {
            public Document document { get; private set; }
            public Node nextnode { get; private set; }

            public Node(string strType, string strName)
            {
                document = new Document(strType, strName);
            }

            public void setNext(Node node)
            {
                nextnode = node;
            }
            
            public class Document
            {
                public string Type { get; private set; }
                public string Name { get; private set; }

                public Document(string strType, string strName)
                {
                    Name = strName;
                    Type = strType;
                }
            }
        }
    }
}

PrintQueue pq = new PrintQueue();
pq.Push("cpp", "main.cpp");
pq.Push("c#", "main.cs");
pq.Push("c", "main.c");
pq.Push("h", "myinclude.h");

Console.WriteLine(pq.DisplayContents());
Console.WriteLine("===");

PrintQueue.Node.Document doc;
doc = pq.Pop();
Console.WriteLine("{0}: {1}", doc.Name, doc.Type);
doc = pq.Pop();
Console.WriteLine("{0}: {1}", doc.Name, doc.Type);
doc = pq.Pop();
Console.WriteLine("{0}: {1}", doc.Name, doc.Type);
doc = pq.Pop();
Console.WriteLine("{0}: {1}", doc.Name, doc.Type);
Console.WriteLine("===");

Console.WriteLine(pq.DisplayContents());
Console.WriteLine("===");

pq.Push("xls", "workbook.xls");
Console.WriteLine(pq.DisplayContents());

content = node.document.Name + ": " + node.document.Type;
while (node.nextnode != null)
{
    node = node.nextnode;
    content += "\r\n" + node.document.Name + ": " + node.document.Type;
}

while (node.nextnode != null)
{
    content += node.document.Name + ": " + node.document.Type + "\r\n";
    node = node.nextnode;
}

public string DisplayContents()
{
    StringBuilder content = new StringBuilder();
    Node node = head;
    while (node != null)
    {
        content.AppendFormat("{0} : {1}\n", node.document.Name, node.document.Type);
        node = node.nextnode;
    }
    return content.ToString();
}

var forma = new FormA();
txtQtyB.Text = forma.panelA.txtQtaA.Text;

var forma = new FormA();
txtQtyB.Text = forma.txtQtaA.Text;