使用小数时得到 System.FormatException，好像我不应该

Question

我需要制作一个 "banking" 程序，除了一个问题外，我已经设置好它并开始工作了。当我试图提取比帐户中更多的钱时，我不断收到 System.FormatException 告诉我 "input string was not in correct format"。我正在使用十进制变量，当我在文本框中输入 101 以从包含 100 美元的帐户中提取时，我得到了异常。

我想警告用户他们没有足够的资金，然后将账户金额恢复到他们试图取款之前的金额为负数。我该怎么办？我在很多地方都在网上看过，但在这件事上没有找到太多帮助。另外请对我放轻松，我对编程还是很陌生。

ps。当存款或取款不为负数时，这不是问题，只有当账户为负数时才会出现异常。

if (amount < 0m)
        {
            amount += Decimal.Parse(textBox1.Text); // this is where the error occurs 
            MessageBox.Show("invalid funds");
        }

完整代码在这里

 Decimal amount = 0.00m;
    public Form1()
    {
        InitializeComponent();
    }

    private void Deposit_Click(object sender, EventArgs e)
    {
            try
            {

                //checks for a user input below or equal to 1000 and greater than 0
                if (Decimal.Parse(textBox1.Text) <= 1000 && Decimal.Parse(textBox1.Text) > 0)
                {
                    amount += Decimal.Parse(textBox1.Text);
                    textBox1.Text = "";
                }
            else
            {
                {
                    // shows when ever a user trys to deposit anything other than a valid number
                    MessageBox.Show("Please enter an amount between [=12=] - ,000.");
                    textBox1.Text = "";
                }
            }
            }

            // catches exceptions when the user trys to deposit anything other than a valid number
            catch
            {
                MessageBox.Show("Please enter an amount between [=12=] - ,000.");
                textBox1.Text = "";
            }
    }

    private void Account_Click(object sender, EventArgs e)
    {
        textBox1.Text = string.Format("$" + amount.ToString());
    }

    private void Withdrawal_Click(object sender, EventArgs e)
    {
        try
        {

            //checks for a user input below or equal to 1000
            if (Decimal.Parse(textBox1.Text) <= 1000 && Decimal.Parse(textBox1.Text) > 0)
            {
                amount -= Decimal.Parse(textBox1.Text);
                textBox1.Text = "";
            }
            else
            {
                {
                    // shows when ever a user trys to withdrawal anything other than a valid number
                    MessageBox.Show("Please enter an amount between [=12=] - ,000.");
                    textBox1.Text = "";
                }
            }
        }

        // catches exceptions when the user trys to withdrawal anything other than a valid number
        catch
        {
            MessageBox.Show("Please enter an amount between [=12=] - ,000.");
            textBox1.Text = "";
        }

        //checks to see if the user has withdrawn the account below 0
        if (amount < 0m)
        {
            amount += Decimal.Parse(textBox1.Text);
            MessageBox.Show("invalid funds");
        }
    }


    //clears the text box for a new entry when the user click on it
    private void textBox1_TextChanged(object sender, EventArgs e)
    {
        textBox1.Text = "";
    }

Answer 1

有时让 textBox1 输出美元符号 (Account_Click) 可能对您没有帮助，但在其他时候它应该 而不是 有美元符号（只是数字在 Withdrawal_Click).

这种事情搅乱了局面，不仅使应用程序的使用变得混乱，而且在调试它时也会使您感到困惑 - 也许在这种情况下不会，但在您编写更复杂的程序时。

出现异常是因为文本框中有一个字符对小数点无效（我猜是 $）。

你想要做的是当 Visual Studio 因异常而停止时，将鼠标悬停在 "textBox1.Text" 上并查看它的值是什么，它是否包含“$”或任何空格？

使用小数时得到 System.FormatException，好像我不应该

Getting a System.FormatException when using a decimal, it seems as though I shouldn't be

c#

exception-handling