Calculator with Stack

using System;

using System.Collections.Generic;

using System.ComponentModel;

using System.Data;

using System.Drawing;

using System.Linq;

using System.Text;

using System.Windows.Forms;

namespace WindowsFormsApplication1

{

    public partial class calc : Form

    {

        public calc()

        {

            InitializeComponent();

        }

        Stack<int> st = new Stack<int>();

        private void button1_Click(object sender, EventArgs e)

        {

            string[] ar = new string[100];

            string fg = textBox1.Text;

            ar = fg.Split('+');

            int total = 0;

            for (int i = 0; i < ar.Length; i++)

            {

                st.Push(Convert.ToInt32(ar[i].ToString()));

                listBox1.Items.Add(ar[i].ToString());

            }

            MessageBox.Show(st.Count.ToString());

            for (int i = st.Count; i > 0; i--)

            {

                int s = st.Pop();

                total = total + s;

            }

            MessageBox.Show(Convert.ToString(total));

        }

    }

}