Question

运行我在'if'语句之间放置的代码时，我的程序失败了。我知道为什么过分依赖一项任务就是检测到数字＆lt; 10或＆gt; 9 高于9的数字有效，但是带有一位数的数字将导致此位置出现异常：

            str = textBox23.Text;
            retString = str.Substring(1, 1);
            textBox22.Text = retString;

我猜测if / else编写得不好，但是我已经检查了不同的变量，但它没有用。我真的不知道发生了什么这是代码：

private void button10_Click_1(object sender, EventArgs e)
{

    if (textBox23.Text == "" || Int32.Parse(textBox23.Text) > 9)

    {
        double L1 = double.Parse(textBox13.Text);
        double L2 = double.Parse(textBox16.Text);
        double wynik = L1 - L2;
        textBox23.Text = wynik.ToString();

        string str = null;
        string retString = null;
        str = textBox23.Text;
        retString = str.Substring(0, 1);
        textBox21.Text = retString;

        str = textBox23.Text;
        retString = str.Substring(1, 1);
        textBox22.Text = retString;

    }

    else if (textBox23.Text == "" || Int32.Parse(textBox23.Text)
    < 10)
    {
        double L1 = double.Parse(textBox13.Text);
        double L2 = double.Parse(textBox16.Text);
        double wynik = L1 - L2;
        textBox23.Text = wynik.ToString();

        string str = null;
        string retString = null;
        str = textBox23.Text;
        retString = str.Substring(0, 1);
        textBox21.Text = retString;

    }

Answer 1

您正在更改textbox23的值

textBox23.Text = wynik.ToString();

任何机会这个值都不是2个字符长，因为后者你做

str = textBox23.Text;
retString = str.Substring(1, 1);

由于substring是从零开始的字符，如果它不是至少2个字符，你会得到一个错误

Answer 2

你可以使用tryParse

private void button10_Click_1(object sender, EventArgs e)
{
   Int32 IsAnumber;
if(Int32.TryParse(textBox23.Text, out IsAnumber)
{
if (IsAnumber > 9)

{
    double L1 = double.Parse(textBox13.Text);
    double L2 = double.Parse(textBox16.Text);
    double wynik = L1 - L2;
    textBox23.Text = wynik.ToString();

    string str = null;
    string retString = null;
    str = textBox23.Text;
    retString = str.Substring(0, 1);
    textBox21.Text = retString;

    str = textBox23.Text;
    retString = str.Substring(1, 1);
    textBox22.Text = retString;

}

else 
{
    double L1 = double.Parse(textBox13.Text);
    double L2 = double.Parse(textBox16.Text);
    double wynik = L1 - L2;
    textBox23.Text = wynik.ToString();

    string str = null;
    string retString = null;
    str = textBox23.Text;
    retString = str.Substring(0, 1);
    textBox21.Text = retString;

}
}

Answer 3

不清楚你想要获得什么，但是我会选择这个

int int23 = 0;

if (!int.TryParse(textBox23.Text, out int23)) 
{
   // manage error and exit function (via exception or return), test in here also string.Empty for textBox23.
}

if (int23 > 9) 
{
    // Do What you need
}
else if (int23 < 10) 
{
    // Do What you need
}

但是一旦你得到了int变量，你可以直接格式化它们。

Answer 4

这样的东西看起来与你想要实现的类似

    private void button10_Click_1(object sender, EventArgs e)
    {
        double box23;

        if (double.TryParse(textBox23.Text, out box23))
        {
            double L1 = double.Parse(textBox13.Text);
            double L2 = double.Parse(textBox16.Text);
            double wynik = L1 - L2;
            textBox23.Text = wynik.ToString();

            string str = textBox23.Text;
            string retString = str.Substring(0, 1);
            textBox21.Text = retString;

            if (box23 > 9)
            {
                str = textBox23.Text;
                retString = str.Substring(1, 1);
                textBox22.Text = retString;
            }
        }
    }

if和else在C＃中循环

4 个答案: