问出现不需要的字符

EN

double rat;
byte operations; 

public void TheEqualMinus(double earlier) //Substraction Operation Method
{
     double _minus;
     _minus = Convert.ToDouble(result.Text);

    double last = _minus - earlier;
    result.Text = last.ToString();
}

private void button15_Click(object sender, EventArgs e)
{
    //The Subtract Button
    operations = 2;
    rat = Convert.ToDouble(result.Text);
    label1.Text = rat + " -";
    result.Text = "";
}

private void button4_Click(object sender, EventArgs e)
{
    // equal button
    NewText = true; //boolean to newtext
    switch (operations)
    {
        case (1):   //addition 
            TheEqualSum(rat);
            label1.Text = "";
            break;
        case (2):   //substraction
            TheEqualMinus(rat);
            label1.Text = "";
            break;
    }
}