Как считать только цифры из файла?

private: System::Void btnFile_Click(System::Object^ sender, System::EventArgs^ e) {
    String^ FileName = "";
    txt5->Text = "";
    if (openFileDialog1->ShowDialog() == Windows::Forms::DialogResult::OK) {
        FileName = openFileDialog1->FileName;
        textBox1->Text = openFileDialog1->FileName;
        txt1->Text = "";
        txt2->Text = "";
        txt3->Text = "";
    }
    try {
        StreamReader^ file = File::OpenText(FileName);
        txt4->Text = file->ReadToEnd();
    }
    catch (Exception^ e) {
        MessageBox::Show(this, "Файл не найден", "Ошибка", MessageBoxButtons::OK, MessageBoxIcon::Error);
    }
}
private: System::Void btnSave_Click(System::Object^ sender, System::EventArgs^ e) {
    SaveFileDialog^ saveFileDialog1 = gcnew SaveFileDialog();
    saveFileDialog1->Filter = "TextFiles (*.txt)|*.txt|All files(*.*)|*.*";
    saveFileDialog1->FilterIndex = 1;
    saveFileDialog1->RestoreDirectory = true;
    saveFileDialog1->CreatePrompt = true;
    saveFileDialog1->OverwritePrompt = true;
    saveFileDialog1->FileName = Convert::ToString(textBox2->Text);
    saveFileDialog1->InitialDirectory = "C:\Users\79266";
    if (saveFileDialog1->ShowDialog() == System::Windows::Forms::DialogResult::OK){
        System::IO::File::WriteAllText(saveFileDialog1->FileName, txt5->Text);
    }
}