C＃如何在每次单击时使用文本框减去并在另一个文本框中显示

Question

我想在每次单击减法按钮时减去，现在它所做的只是减去一次。我猜它总是将所需的值视为4000，这就是为什么它不会多次减去它，因为每次点击都会检索到初始需要的值。

int needed = 4000;
private void subtractBtn_Click(object sender, EventArgs e)
    {
        int Subtract = Convert.ToInt32(textBox_Subtract.Text);
        remaining = needed - Subtract;
        textBox_Remaining.Text = remaining.ToString();

        if (remaining <=0)
        {
            MessageBox.Show("Hey it's done");
        }
    }

对于像我这样愚蠢的人来说，最后的代码是

private void subtractBtn_Click(object sender, EventArgs e)
    {
        int Subtract = Convert.ToInt32(textBox_Subtract.Text);

        remaining = needed - Subtract;
        needed = remaining;


        textBox_Remaining.Text = remaining.ToString();

        if (remaining <=0)
        {
            MessageBox.Show("Hey it's done");
        }
    }

Answer 1

private void subtractBtn_Click(object sender, EventArgs e)
{
    int Subtract = Convert.ToInt32(textBox_Subtract.Text);
    remaining = needed - Subtract;
    needed = remaining;
    textBox_Remaining.Text = remaining.ToString();

    if (remaining <=0)
    {
        MessageBox.Show("Hey it's done");
    }
}