計算e號C＃

Question

我試圖計算e數

e = 1 + (1/1! + 1/2! + 1/3! + ..)

用戶將在該表單上選擇試驗次數。 形成

 int trialNumber = Convert.ToInt32(Math.Round(trialNumberForm.Value, 0));
        int factorial = trialNumber;
        float factResult = 0;

        for (int i = 1; i < trialNumber; i++)
        {

            for (int b = 1; b < i; b++) //calculates x! here.
            {
                factorial = factorial * b;


            }
           factResult = factResult + (1 / factorial);
        }
        factResult++;
        MessageBox.Show(factResult.ToString());

它會計算您選擇的結果1！ 我試圖將變量類型從double更改為float但是沒有修復它。 如何根據我上面寫的公式對數字采取行動？

Answer 1

你根本不需要因子（具有整數除法和整數溢出問題）

  1/(n+1)! == (1/n!)/(n+1)

您可以輕松實現e計算

  double factResult = 1; // turn double into float if you want
  double item = 1;       // turn double into float if you want

  for (int i = 1; i < trialNumber; ++i)
    factResult += (item /= i);

  ...

  MessageBox.Show(factResult.ToString());

成果：

   trial number | e
   -------------------------------
              1 | 1
              2 | 2
              3 | 2.5
              4 | 2.666666... 
              5 | 2.708333...
             10 | 2.71828152557319
             15 | 2.71828182845823 
             20 | 2.71828182845905

Answer 2

正如@kabdulla和@ScottChamberlain所說，你正在進行整數除法，你需要一個浮點除法：

for (int b = 1; b < i; b++) //calculates x! here.
{
    factorial = factorial * b;
}
factResult = factResult + (1 / factorial);

應該

for (int b = 2; b < i; b++) //calculates x! here.
{
    factorial = factorial * b;
}
factResult = factResult + (1.0 / factorial);

另外，我在b = 2開始for循環，因為乘以1是沒用的。