如何检查素数 [英] How to check for prime numbers

问题描述

以下代码列出了从 1 到 10 的所有质数:

The following code lists all prime numbers from 1 to 10:

Dim primeN As Integer 
Dim primeI As Integer
Dim primeFlag As Boolean

For primeN = 1 To 10
    primeFlag = True
    For primeI = 2 To primeN / 2
       If primeN Mod primeI = 0 Then
         primeFlag = False
       End If
    Next
    If primeFlag Then
       Console.WriteLine(primeN)
    End If
Next
Console.ReadLine()

如何更改它以使其读取用户输入，然后检查它是否为质数?

How can I change it so that it reads the user input and then checks if it's a prime number?

推荐答案

这是我检查数字是否为质数的最快 VBA 代码.

This is my fastest VBA code to check if a number is a prime number.

Sub ISPRIME()
Dim number_to_be_checked As Long
Dim c As Long
Dim b As Long
number_to_be_checked = 2000000000 'input value here
c = Round(Sqr(number_to_be_checked)) + 1
If number_to_be_checked = 1 Then
    MsgBox "Not Prime"
Else
    For b = 2 To c
        If number_to_be_checked Mod b = 0 And c <> b Then
            MsgBox "Not Prime. Divisible by " & b
            Exit Sub
        Else
            If b = c Then
                MsgBox "Prime"
                Exit Sub
            End If
        End If
    Next b
End If
End Sub

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