how to send data from one form to another

using System;
using System.Collections;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;

namespace AllsortingTechs
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void Form1_Load(object sender, EventArgs e)
        {

        }

        private void btnsortitems_Click(object sender, EventArgs e)
        {
            
            String[] items = txtBox1.Text.Split(',');
            ArrayList sitems = new ArrayList();
            ArrayList ritems = new ArrayList();
            foreach(string input in items)
            sitems.Add(input);

            if (rbnGeneral.Checked)
            {
                ritems = Generalsort(sitems);
               

            }

            if (rbnBubble.Checked)
                ritems = Bubblesort(sitems);

            if (rbnStraightInsertion.Checked)
                ritems = Insertionsort(sitems);


            if (rbnStraightExchange.Checked)
                ritems = StraightExchange(sitems);

            

             }
        private ArrayList Generalsort(ArrayList sitems)
        {
            lstbox1.Items.Clear();
            int n = sitems.Count;
            Object temp;
           lstbox1.Items.Add("generalsort");

            for (int i = 0; i < n; i++)
            {
                for (int j = 1+i; j < n; j++)
                {
                    if (Convert.ToInt32(sitems[i]) > Convert.ToInt32(sitems[j]))// here getting exception
                    {
                        temp = sitems[i];
                        sitems[i] = sitems[j ];
                        sitems[j ] = temp;
                    }

                }
                
                lstbox1.Items.Add(sitems[i]);
            }
            

            return sitems;


        }
      


        private ArrayList Bubblesort(ArrayList sitems)  
        {
            lstbox1.Items.Clear();
            int n = sitems.Count;
            Object temp;
            lstbox1.Items.Add("bubblesort");

            for (int i = 0; i < n; i++)
            {
                for (int j = 0; j < n - i - 1; j++)
                {
                    if (Convert.ToInt32(sitems[j]) > Convert.ToInt32(sitems[j + 1]))// here getting exception
                    {
                        temp = sitems[j];
                        sitems[j] = sitems[j + 1];
                        sitems[j + 1] = temp;
                    }

                }

            }
                for (int i = 0; i < n; i++)
                {

                   lstbox1.Items.Add(sitems[i]);
                }
                               
               return sitems; 
                

            }
        public ArrayList StraightExchange(ArrayList sitems)
        {
            lstbox1.Items.Clear();
            lstbox1.Items.Add("exchangesort");
            int n = sitems.Count;
            for (int i = 0; i < n; i++)
            {
                object small = sitems[i];
                int pos = i;
                for (int j = i + 1; j < n; j++)
                {

                    if (Convert.ToInt32(sitems[j]) < Convert.ToInt32(small))
                    {
                        small = sitems[j];
                        pos = j;
                    }
                }
                sitems[pos] =sitems[i];
                sitems[i] = small;

               lstbox1.Items.Add(sitems[i]);
            }
            return sitems;
        }

        public ArrayList Insertionsort(ArrayList sinputs)
        {
            lstbox1.Items.Clear();
            lstbox1.Items.Add("insertionsort");
            int n = sinputs.Count;
            for (int i = 0; i < n; i++)
            {
                object small = sinputs[i];
                int pos = i;
                for (int j = i + 1; j < n; j++)
                {
                    if (Convert.ToInt32(sinputs[j]) < Convert.ToInt32(small))
                    {
                        small = sinputs[j];
                        pos = j;
                    }
                }
                for (int k = pos; k > i; k--)
                {
                    sinputs[k] = sinputs[k - 1];
                }
                sinputs[i] = small;

                lstbox1.Items.Add(sinputs[i]);
            }
            return sinputs;
        }

        private void txtBox1_TextChanged(object sender, EventArgs e)
        {

        }
        }

       }