c# - 如何写出用于计算阶乘的所有整数

Question

现在我有 4! = 24 被输出到消息框。

我想做的是将计算 n 时乘以的所有整数相加。所以如果我输入 4，我想得到 4! = 1 x 2 x 3 x 4 = 24，而不是 4! = 24。

代码:

private void calculateButton_Click(object sender, EventArgs e)
{
    int userNumber = 0;
    double factorialNumber = 1;

    int.TryParse(numberInputTextBox.Text, out userNumber);

    if (userNumber > 0)
    {
        for (int countFactorial = 1; countFactorial <= userNumber; countFactorial++)
        {
            factorialNumber *= countFactorial;
        }

        MessageBox.Show(userNumber + "! = " + factorialNumber.ToString("n0"));
        resetButton.Focus();
    }
    else
    {
        MessageBox.Show("The factorial value entered must be an integer.");
        numberInputTextBox.Text = "";
        numberInputTextBox.Focus();
    }
}

Answer 1

您可以输入从 1 到 userNumber 的数字进入 List<int> nums (例如)然后使用 var numsStr = string.Join(" x ", nums);获取字符串 1 x 2 x 3 x 4

例子:

if (userNumber > 0)
    {
        List<int> nums = new List<int>();
        for (int countFactorial = 1; countFactorial <= userNumber; countFactorial++)
        {
            factorialNumber *= countFactorial;
            nums.Add(countFactorial);
        }
        
        var numsStr = string.Join(" x ", nums);            
        var result = string.Format("{0} ! = {1} = {2}", userNumber, numsStr, factorialNumber.ToString("n0"));
        MessageBox.Show(result);
        resetButton.Focus();
    }