IsPrimeNumber function

[/\/\1|<3]

here it is:

Func IsPrimeNumber($num)
   If IsNumber($num) = 0 Or $num = 0 Then
      Return -1
   Else
      
      Local $pnum = 0
      Local $npnum = 0
      Local $i
      
      $i = 2
      While $i < Int($num)
         $ch = $num / $i
         $i = $i + 1
         If $ch = Int($ch) Then
            $npnum = 1
         Else
            $pnum = 1
         EndIf
      WEnd
      If $num = 2 Then
         Return 1
      ElseIf $npnum = 1 And $num <> 2 Then
         Return 0
      ElseIf $pnum = 1 And $npnum = 0 Then
         Return 1
      EndIf
   EndIf
EndFunc

it checks if a number is a prime number. if it is, the function returns 1, if not it returns 0. if you insert a string or 0 (which is not a real number) it returns -1

Mike

Edited December 26, 2004 by /\/\1|<3

[phillip123adams]

here it is:

Func IsPrimeNumber($num)
   If IsNumber($num) = 0 Or $num = 0 Then
      Return -1
   Else
      
      Local $pnum = 0
      Local $npnum = 0
      
      $i = 2
      While $i < Int($num)
         $ch = $num / $i
         $i = $i + 1
         If $ch = Int($ch) Then
            $npnum = 1
         Else
            $pnum = 1
         EndIf
      WEnd
      If $num = 2 Then
         Return 1
      ElseIf $npnum = 1 And $num <> 2 Then
         Return 0
      ElseIf $pnum = 1 And $npnum = 0 Then
         Return 1
      EndIf
   EndIf
EndFunc

it checks if a number is a prime number. if it is, the function returns 1, if not it returns 0. if you insert a string or 0 (which is not a real number) it returns -1

NOTE: there´s a problem with it. see this

Mike

<{POST_SNAPBACK}>

Global got you! Add Local $i to the Func.

[/\/\1|<3]

big thanks

edited it

Mike

[Insolence]

You have to use Local for variables inside funcs?

[/\/\1|<3]

somtimes

if your script says something like "variable undeclared" but you´re sure that you declared it, then use Local. but i´d always use it in functions to avoid errors

Mike.

[Jos]

somtimes  

if your script says something like "variable undeclared" but you´re sure that you declared it, then use Local. but i´d always use it in functions to avoid errors 

Mike.

<{POST_SNAPBACK}>

It is a good practice to always define variables that are only used inside the Func...EndFunc as Local.

I think what is meant here is that you didn't define $I as LOCAL....

Edited December 26, 2004 by JdeB

[ezzetabi]

Actually 0 is a real number...

But the point of this post is an other interesting way to check is a number is prime or not.

Being p the number that you want checking

p is prime if

(p-1)! = [-1]

That it means the modulus of (p-1)! dividing by p is (p-1)

E.g. lets check 7

7-1 = 6

6! = 720

720 = 102 * 7 + 6

6 is the modulus that is equal to 7 - 1. 7 is prime.

Of course calculating the ! of big numbers 'may' be a problem so this is not very confortable...

Yet...

This is my way.

MsgBox(0,'',_IsPrime(4999))

Func _IsPrime($sNum)
   If $sNum = 0 Then Return -1
   
   $sNum = Int($sNum)
   If $sNum < 0 Then $sNum = $sNum * -1
      
   Local $c, $bPrime = 1
   
   If $sNum > 2 Then
   For $c = 2 to Int($sNum ^ (1/2)+1)
      If Mod($sNum,$c) = 0 Then
         $bPrime = 0
         ExitLoop
      EndIf
   Next
   EndIf
   
   Return $bPrime
EndFunc

About the advices you got I'll add one. When you code use always

Opt ('MustDeclareVars', 1)

Overall if you want to share your functions!

Edited December 27, 2004 by ezzetabi

[abel]

hello ezzetabi,

what do you think about checking only the odd factors greater than 2?

MsgBox(0,'',_IsPrime(4999))

Func _IsPrime($sNum)
   If $sNum = 0 Then Return -1
   
   $sNum = Int($sNum)
   If $sNum < 0 Then $sNum = $sNum * -1
      
   Local $c, $bPrime = 1
   
   If $sNum > 2 Then
   If Mod($sNum,2) = 0 Then Return 0
   For $c = 3 to Int($sNum ^ (1/2)+1) Step 2
      If Mod($sNum,$c) = 0 Then
         $bPrime = 0
         ExitLoop
      EndIf
   Next
   EndIf
   
   Return $bPrime
EndFunc

Your way to check if a number is prim or not using the ! is very interesting.

I never saw this method before.

abel

[LazyCoder]

Let's say P is the number.

In fact, the best "common" way is to test (decending order) all dividers lower than int(sqrt(P)) as at most P=(sqrt(P))^2, avoiding all even factors.

Of course, you can easily check that P can't be simply divided by 2...

You'll save time this way...

[ezzetabi]

The best is testing the modulus of all prime numbers smaller or equal than the square root (rounded to the next int) than the number you have to check.

More or less as I did in my

udf for finding prime numbers.