为什么这个计算器给我 'Input string was not in correct format' 错误？

Question

我正在使用 System.Windows.Forms 来计算这个计算器，每次我尝试进行平方根、余弦、正弦或正切运算并按下等于按钮时，它会停止并告诉我 'System.FormatException : Input string was not in a correct format' 并且我不知道为什么。

这是我的 buttonEquals_Click 活动：

private void buttonEquals_Click(object sender, EventArgs e)
{
    double num2;
    double answer;

    num2 = double.Parse(textBoxResult.Text);

    switch (theOperator)
    {
        case "+":
            answer = resultValue + num2;
            textBoxResult.Text = answer.ToString();
            resultValue = 0;
            break;
        case "-":
            answer = resultValue - num2;
            textBoxResult.Text = answer.ToString();
            resultValue = 0;
            break;
        case "×":
            answer = resultValue * num2;
            textBoxResult.Text = answer.ToString();
            resultValue = 0;
            break;
        case "÷":
            answer = resultValue / num2;
            textBoxResult.Text = answer.ToString();
            resultValue = 0;
            break;
        case "sqrt":
            answer = Math.Sqrt(resultValue);
            textBoxResult.Text = answer.ToString();
            resultValue = 0;
            break;
        case "exp":
            answer = Math.Pow(resultValue, num2);
            textBoxResult.Text = answer.ToString();
            resultValue = 0;
            break;
        case "sin":
            answer = Math.Sin(resultValue);
            textBoxResult.Text = answer.ToString();
            resultValue = 0;
            break;
        case "cos":
            answer = Math.Cos(resultValue);
            textBoxResult.Text = answer.ToString();
            resultValue = 0;
            break;
        case "tan":
            answer = Math.Tan(resultValue); 
            textBoxResult.Text = answer.ToString();
            resultValue = 0;
            break;
        default:
            answer = 0;
            break;
    }
}

这是我的 SqrtButton_Click 事件和 DivisionButton_event（所以你可以看到 DivisionButton 确实有效）：

private void SqrtButton_Click(object sender, EventArgs e)
{
    resultValue = resultValue + double.Parse(textBoxResult.Text);
    theOperator = "sqrt";
    textBoxResult.Clear();
}

private void DivisionButton_Click(object sender, EventArgs e)
{
    resultValue = resultValue + double.Parse(textBoxResult.Text);
    theOperator = "÷";
    textBoxResult.Clear();
}

如有任何帮助，我将不胜感激。

编辑：异常发生在：num2 = double.Parse(textBoxResult.Text);

Answer 1

我猜当你试图测试那些家伙时，textBoxResult 是空的。请注意，您正在执行行 num2 = double.Parse(textBoxResult.Text); 如果最近清除了 textBoxResult，那么您会在此处遇到形式为 System.FormatException : Input string was not in a correct format 的问题（空的 string/null 不会被 double.Parse 作为 0.00)

为什么这个计算器给我 'Input string was not in correct format' 错误？

Why is this calculator giving me 'Input string was not in correct format' Error?

.net

c#

exception

calculator

winforms