好久没来这里了。最近看了一些数论方面的文章，受益匪浅。想到我们初学VB时，利用循环查找素数是必修之课，随手写了两段列举素数的代码，并详细注释。自己感觉还是比较快的。 代码如下：
'*******************************************************************************
' Target:to get all prime numbers smaller than a certain number
' Author：northwolves
' Reference："Sieve of Eratosthenes"
' Createdate：2005-04-18 00:00:00
'*******************************************************************************
Sub showprime1(ByVal max As Long) 'find all prime numbers smaller than max(max>=3)
Dim p() As Long, i As Long, j As Long, number As Long, sqrtmax As Long, beprime As Boolean 'difinations
number = 1
ReDim p(1 To number)
p(1) = 2 ' the unique even prime number
Debug.Print p(1) 'show the first prime number
If max < 3 Then Exit Sub 'since we want do something
For i = 3 To max Step 2 ' skip those even number
sqrtmax = Int(Sqr(i)) + 1 'get the largest non-self factor of i
beprime = True ' init
For j = 1 To number ' try all primer numbers we have found before.
If i Mod p(j) = 0 Then beprime = False: Exit For 'not a prime number
If p(j) > sqrtmax Then Exit For 'unless we'll waste our time
Next
If beprime = True Then ' then it is a prime number
number = number + 1 'add to it's count
ReDim Preserve p(1 To number) 'define again
p(number) = i
Debug.Print i ' output the prime number
End If
Next
Debug.Print "There are " & number & " prime numbers below " & max ' show some message
End Sub
Private Sub Command1_Click() ' show all prime numbers smaller than 100000
showprime1 100000
End Sub
'************************************************************************
' Target:to get the first n prime numbers from 2,3,....
' Author：northwolves
' Reference："Sieve of Eratosthenes"
' Createdate：2005-04-18 00:00:00
'************************************************************************
Sub showprime2(ByVal n As Long) ' get the first n(n>1) prime numbers
Dim p() As Long, i As Long, j As Long, number As Long, sqrtmax As Long, beprime As Boolean
number = 1
ReDim p(1 To number)
p(1) = 2 ' the unique even prime number
Debug.Print 2 'show the first prime number
If n < 2 Then Exit Sub 'since we want do something
i = 3
Do While number <= n
sqrtmax = Int(Sqr(i)) + 1 'get the largest non-self factor of max
beprime = True ' init
For j = 1 To number ' try all primer numbers we have found before.
If i Mod p(j) = 0 Then beprime = False: Exit For 'not a prime number
If p(j) > sqrtmax Then Exit For 'unless we'll waste our time
Next
If beprime = True Then ' then it is a prime number
number = number + 1 'add to it's count
ReDim Preserve p(1 To number) 'define again
p(number) = i
Debug.Print i ' output the prime number
End If
i = i + 2 ' skip those even number
Loop
Debug.Print "The " & n & " prime Number Is " & p(number); "" ' show some message
End Sub
Private Sub Command2_Click() ' show the first 1000 prime numbers
showprime2 1000
End Sub