internal class LIFO : Stack, IDataStruture
    {
        public void Add(T item)
        {
            this.Push(item);
        }
        public T Remove()
        {
           return this.Pop();
        }
    }

   internal class FIFO : Queue, IDataStruture
    {
        public void Add(T item)
        {
            this.Enqueue(item);
        }
        public T Remove()
        {
           return this.Dequeue();
        }
    } 

public interface IDataStruture
    {
        void Add(T item);
        T Remove();
    }

    public class Adapter
    {
        private IDataStruture objStack = new LIFO();
        private IDataStruture objQueue = new FIFO();

        public void AddLIFO(T item)
        {
            objStack.Add(item);            
        }
        public void AddFIFO(T item)
        {            
            objQueue.Add(item);
        }
        public T RemoveLIFO()
        {
            return Remove(objStack);
        }
        public T RemoveFIFO()
        {
            return Remove(objQueue);
        }
        private T Remove(IDataStruture ds)
        {
            T item;
            item = ds.Remove();
            return item;
        }       
        
    }

Adapter adapter;
        public Form1()
        {
            InitializeComponent();
            adapter = new Adapter();            
        }

private void btnPush_Click(object sender, EventArgs e)
        {
            if (comboBox1.Text.Equals("LIFO"))            
                foreach (string str in lstPush.CheckedItems)
                {
                    adapter.AddLIFO(str);
                }
            else            
                foreach (string str in lstPush.CheckedItems)
                {
                    adapter.AddFIFO(str);
                }            
        }

        private void btnPop_Click(object sender, EventArgs e)
        {
            if (comboBox1.Text.Equals("LIFO"))
             lstPop.Items.Add(adapter.RemoveLIFO());
            else
              lstPop.Items.Add(adapter.RemoveFIFO());
        }