private void subtractButton_Click(object sender, EventArgs e)
{
Initialization();
result = aCalculator.Subtract(firstNumber, secondNumber);
resultTextBox.Text = result.ToString();
}
private void subtractButton_Click(object sender, EventArgs e)
{
aCalculator.firstNumber = Convert.ToDouble(firstNumberTextBox.Text);
aCalculator.secondNumber = Convert.ToDouble(secondNumberTextBox.Text);
resultTextBox.Text = aCalculator.Subtract().ToString();
}