OpenFileDialog

void FileProc(StreamReader^ sr, StreamWriter^ sw, ListBox^ lstInFile, ListBox^ lstOutFile, TextBox^ mincountTB) {
    String^ InBuffer = "";
    String^ OutBuffer = "";
    int count = 0;                          // Количество изменений в строке
    int mincount = 1000000;                 // Минимальное количество изменений
    String^ mincountString = "";            // Строка с минимальным количеством изменений
    try {
        while (InBuffer = sr->ReadLine()) {
            if (InBuffer->Length == 0) continue;
            lstInFile->Items->Add(InBuffer);
            count = 0;                          // Количество изменений в строке
            OutBuffer = task(InBuffer, count);
            sw->WriteLine(OutBuffer);
            lstOutFile->Items->Add(OutBuffer);
            if (count < mincount && count > 0) { // Поиск строки с минимальным количеством изменений
                mincount = count;
                mincountString = OutBuffer;
            }
        }
        if (mincountString == "") mincountString = "Изменений не было.";
        mincountTB->Text = mincountString;
    }
    catch (Exception ^ ex) {
        MessageBox::Show(ex->Message, "Ошибка", MessageBoxButtons::OK, MessageBoxIcon::Error);
    }
}

    private: System::Void Button_Start_Click(System::Object^ sender, System::EventArgs^ e) {
        listBox_input->Items->Clear();
        listBox_output->Items->Clear();
        String^ InFile = textBox_input->Text;
        String^ OutFile = textBox_output->Text;
        StreamReader^ sr = nullptr;
        StreamWriter^ sw = nullptr;
        try {
            sr = gcnew StreamReader(InFile);
            sw = gcnew StreamWriter(OutFile, false);
        }
        catch (Exception ^ ex) {
            MessageBox::Show(ex->Message, "Ошибка", MessageBoxButtons::OK, MessageBoxIcon::Error);
            if (sr) sr->Close();
            if (sw) sw->Close();
            return;
        }
        FileProc(sr, sw, listBox_input, listBox_output, textBox_mincount);
        sr->Close();
        sw->Close();

    }

private: System::Void Form1_Load(System::Object^ sender, System::EventArgs^ e) {
    listBox_input->Items->Clear();
    listBox_output->Items->Clear();
    textBox_input->Clear();
    textBox_output->Clear();
    button_Start->Enabled = false;
}
private: System::Void Button_openInput_Click(System::Object^ sender, System::EventArgs^ e) {
    OpenFileDialog^ openFileDialog = gcnew OpenFileDialog;
    openFileDialog->Title = "Открытие входногого файла";
    openFileDialog->InitialDirectory = "C:\\";
    openFileDialog->Filter = "Text files (*.txt)|*.txt";
    openFileDialog->FilterIndex = 1;
    openFileDialog->ShowReadOnly = true;
    openFileDialog->ReadOnlyChecked = true;
    openFileDialog->RestoreDirectory = true;
    if (openFileDialog->ShowDialog() == System::Windows::Forms::DialogResult::OK) textBox_input->Text = openFileDialog->FileName;
    else  textBox_input->Text = "";
    button_Start->Enabled = textBox_input->Text->Length > 0 && textBox_output->Text->Length > 0;
}

private: System::Void Button_openOutput_Click(System::Object^ sender, System::EventArgs^ e) {
    SaveFileDialog^ saveFileDialog = gcnew SaveFileDialog;
    saveFileDialog->Title = "Открытие выходногого файла";
    saveFileDialog->Filter = "Text files (*.txt)|*.txt";
    saveFileDialog->FilterIndex = 1;
    saveFileDialog->OverwritePrompt = true;
    if (saveFileDialog->ShowDialog() == System::Windows::Forms::DialogResult::OK) textBox_output->Text = saveFileDialog->FileName;
    else  textBox_input->Text = "";
    button_Start->Enabled = textBox_input->Text->Length > 0 && textBox_output->Text->Length > 0;
}