C# Алгоритм Карпа-Рабина

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

namespace lab_44
{
    public partial class Form1 : Form
    {
        public int Text_func (string required_text, string all_text)
        {
            char[] temp0 = required_text.ToCharArray();
            string temp1 = "";
            char[] temp_all_text;
            int counter = 0;
            temp_all_text = all_text.ToCharArray();

            for (int i = 0; i < temp_all_text.Length; i++)
            {
                for (int j = 0; j < required_text.Length; j++)
                {
                    temp1 += temp_all_text[j];
                }
                if (temp1 == required_text)
                {
                    counter++;
                    temp1 = "";
                    //изменяет найденный текст на БОЛЬШОЙ
                    //all_text.Substring(i, required_text.Length) = all_text.Substring(i, required_text.Length).ToUpper();
                }
            }
            return counter;
        }
        public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click_1(object sender, EventArgs e)
        {
            Stream myStream = null;
            OpenFileDialog openFileDialog1 = new OpenFileDialog();

            openFileDialog1.InitialDirectory = "c:\\";
            openFileDialog1.Filter = "txt files (*.txt)|*.txt|All files (*.*)|*.*";
            openFileDialog1.FilterIndex = 2;
            openFileDialog1.RestoreDirectory = true;

            if (openFileDialog1.ShowDialog() == DialogResult.OK)
            {
                try
                {
                    if ((myStream = openFileDialog1.OpenFile()) != null)
                    {
                        using (myStream)
                        {
                            // Insert code to read the stream here.
                            StreamReader sr = new StreamReader(openFileDialog1.FileName);
                            textBox1.Text = sr.ReadToEnd();
                            

                            textBox3.Text = Text_func(textBox2.Text, sr.ReadToEnd()).ToString();
                            //textBox1.Text = myStream.ToString();
                            sr.Close();
                        }
                    }
                }
                catch (Exception ex)
                {
                    MessageBox.Show("Error: Could not read file from disk. Original error: " + ex.Message);
                }
            }
        }





        private void textBox1_TextChanged(object sender, EventArgs e)
        {

        }

        private void textBox2_TextChanged(object sender, EventArgs e)
        {

        }

        private void textBox3_TextChanged(object sender, EventArgs e)
        {

        }
    }
}

public int Text_func (string required_text, string all_text)
        {
            int counter = 0;//количество вхождений
            while (all_text.Contains(required_text))
            {
                all_text.Remove(all_text.IndexOf(required_text), required_text.Length);
                counter++;
            }
            return counter;
        }

all_text = all_text.Remove(all_text.IndexOf(required_text), required_text.Length);

StreamReader sr = new StreamReader(openFileDialog1.FileName);
textBox1.Text = sr.ReadToEnd(); // после этого оператора sr стаёт пустым, по крайней мере если поменять строчки местами, то подсчёт будет вестись:)
textBox3.Text = Text_func(textBox2.Text, sr.ReadToEnd()).ToString();