# _isprime Function

37 replies to this topic

### #1 RazerM

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Posted 13 April 2006 - 01:05 PM

I made a function to see if a number is prime or not. I was bored This has been updated and the function below does work
AutoIt
```;===============================================================================
;
; Function Name:   _IsPrime
; Description:: Check if a number is prime or not
; Parameter(s): \$i_num - Number to check
; Requirement(s):  None
; Return Value(s): 1 - Number is prime
;                 0 - Number is not prime
;                  -1 - String isn't a number
; Author(s):       RazerM
;
;===============================================================================
;
Func _IsPrime(\$i_num)
If StringIsDigit(\$i_num) = 0 Then Return -1
If \$i_num > 3 Then
If Mod(\$i_num, 2) = 0 Then Return 0
If Mod(\$i_num, 3) = 0 Then Return 0
EndIf
If \$i_num = 1 Then Return 0
Dim \$divisor, \$increment, \$maxdivisor
\$divisor = 5
\$increment = 2
\$maxdivisor = Sqrt(\$i_num) + 1

Do
If Mod(\$i_num, \$divisor) = 0 And \$i_num <> \$divisor Then Return 0
\$divisor = \$divisor + \$increment
\$increment = 6 - \$increment
Until \$divisor > \$maxdivisor
Return 1
EndFunc ;==>_IsPrime```

Edit: updated to most recent code

Edited by RazerM, 19 May 2006 - 03:30 PM.

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### #2 VicTT

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Posted 13 April 2006 - 01:54 PM

There is an infinity of factors to be checked before concluding that a number is prime or not(This can be proven)...Your script is incomplete and thus, useless for any prime number higher or equal to 23...Post_Number++;

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### #3 Wus

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Posted 13 April 2006 - 02:10 PM

I fail to see how this function would work.
You are trying to test for primeness based on a finite set of primes. But seeing as how there are infinite primes that wont work. All I had to do to fool your algorithm was to take the next prime after 19 and square it.

ie:
your function tells me that (23*23) or 529 is prime when its obviously the product of two integers.

Prime tests usually have to test the majority of the values from from i=2 to i=int(sqrt(testVal)) +1 for divisability.

This can be seen here http://www.devx.com/vb2themax/Tip/19051

### #4 RazerM

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Posted 13 April 2006 - 03:41 PM

thanks for the feedback guys. Based on that site Wus i made this
Plain Text
```;===============================================================================
;
; Function Name:   _IsPrime
; Description:: Check if a number is prime or not
; Parameter(s): \$i_num - Number to check
; Requirement(s):  Math.au3
; Return Value(s): 1 - Number is prime
;                  0 - Number is not prime
; Author(s):       RazerM
;
;===============================================================================
;
Func _IsPrime(\$i_num)
If \$i_num > 3 Then
If Mod(\$i_num, 2) = 0 Then Return 0
If Mod(\$i_num, 3) = 0 Then Return 0
EndIf
Dim \$divisor, \$increment, \$maxdivisor
\$divisor = 5
\$increment = 2
\$maxdivisor = Sqrt(\$i_num) + 1

Do
If Mod(\$i_num, \$divisor) = 0 Then Return 0
\$divisor = \$divisor + \$increment
\$increment = 6 - \$increment
Until \$divisor > \$maxdivisor
Return 1
EndFunc```
It appears to work but it returns 0 when i test 5 and 5 is definetely prime
My Programs:AInstall - Create a standalone installer for your programUnit Converter - Converts Length, Area, Volume, Weight, Temperature and Pressure to different unitsBinary Clock - Hours, minutes and seconds have 10 columns each to display timeAutoIt Editor - Code Editor with Syntax Highlighting.Laserix Editor & Player - Create, Edit and Play Laserix LevelsLyric Syncer - Create and use Synchronised Lyrics.Connect 4 - 2 Player Connect 4 Game (Local or Online!, Formatted Chat!!)MD5, SHA-1, SHA-256, Tiger and Whirlpool Hash Finder - Dictionary and Brute Force FindCool Text Client - Create Rendered ImageMy UDF's:GUI Enhance - Enhance your GUIs visually.IDEA File Encryption - Encrypt and decrypt files easily! File Rename - Rename files easilyRC4 Text Encryption - Encrypt text using the RC4 AlgorithmPrime Number - Check if a number is primeString Remove - remove lots of strings at onceProgress Bar - made easySound UDF - Play, Pause, Resume, Seek and Stop.

### #5 Daniel W.

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Posted 13 April 2006 - 03:49 PM

Maybe because your Divisor is 5?
I dont know because for me your code is very difficult to understand ( i am newbie atm )
--------------------------------------------------------------------------------------------------------------------------------Scripts : _Encrypt UDF_UniquePCCode UDF MS like calculatorInstall programm *UPDATED* --------------------------------------------------------------------------------------------------------------------------------

Have you ever tried surfing the internet with a milk-carton ?This is similar to what you're trying to do.

### #6 RazerM

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Posted 13 April 2006 - 03:53 PM

Thanks, thats it!
Plain Text
```;===============================================================================
;
; Function Name:   _IsPrime
; Description:: Check if a number is prime or not
; Parameter(s): \$i_num - Number to check
; Requirement(s):  None
; Return Value(s): 1 - Number is prime
;                  0 - Number is not prime
; Author(s):       RazerM
;
;===============================================================================
;
Func _IsPrime(\$i_num)
If \$i_num > 3 Then
If Mod(\$i_num, 2) = 0 Then Return 0
If Mod(\$i_num, 3) = 0 Then Return 0
EndIf
Dim \$divisor, \$increment, \$maxdivisor
\$divisor = 5
\$increment = 2
\$maxdivisor = Sqrt(\$i_num) + 1

Do
If Mod(\$i_num, \$divisor) = 0 And \$i_num <> \$divisor Then Return 0
\$divisor = \$divisor + \$increment
\$increment = 6 - \$increment
Until \$divisor > \$maxdivisor
Return 1
EndFunc  ;==>_IsPrime```

I removed the Math.au3 in requirement and made sure it checked whether the number and the divisor were the same or not before returning 0
My Programs:AInstall - Create a standalone installer for your programUnit Converter - Converts Length, Area, Volume, Weight, Temperature and Pressure to different unitsBinary Clock - Hours, minutes and seconds have 10 columns each to display timeAutoIt Editor - Code Editor with Syntax Highlighting.Laserix Editor & Player - Create, Edit and Play Laserix LevelsLyric Syncer - Create and use Synchronised Lyrics.Connect 4 - 2 Player Connect 4 Game (Local or Online!, Formatted Chat!!)MD5, SHA-1, SHA-256, Tiger and Whirlpool Hash Finder - Dictionary and Brute Force FindCool Text Client - Create Rendered ImageMy UDF's:GUI Enhance - Enhance your GUIs visually.IDEA File Encryption - Encrypt and decrypt files easily! File Rename - Rename files easilyRC4 Text Encryption - Encrypt text using the RC4 AlgorithmPrime Number - Check if a number is primeString Remove - remove lots of strings at onceProgress Bar - made easySound UDF - Play, Pause, Resume, Seek and Stop.

### #7 RazerM

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Posted 13 April 2006 - 04:10 PM

if you use ConsoleWrite on \$increment you will see it alternates between 2 and 4 like it is meant to.

I have updated mine to return 0 if the number is 1
Plain Text
```;===============================================================================
;
; Function Name:   _IsPrime
; Description:: Check if a number is prime or not
; Parameter(s): \$i_num - Number to check
; Requirement(s):  None
; Return Value(s): 1 - Number is prime
;                  0 - Number is not prime
; Author(s):       RazerM
;
;===============================================================================
;
Func _IsPrime(\$i_num)
If \$i_num > 3 Then
If Mod(\$i_num, 2) = 0 Then Return 0
If Mod(\$i_num, 3) = 0 Then Return 0
EndIf
If \$i_num = 1 Then Return 0
Dim \$divisor, \$increment, \$maxdivisor
\$divisor = 5
\$increment = 2
\$maxdivisor = Sqrt(\$i_num) + 1

Do
If Mod(\$i_num, \$divisor) = 0 And \$i_num <> \$divisor Then Return 0
\$divisor = \$divisor + \$increment
\$increment = 6 - Abs(\$increment)
Until \$divisor > \$maxdivisor
Return 1
EndFunc  ;==>_IsPrime```

Edited by RazerM, 13 April 2006 - 04:13 PM.

My Programs:AInstall - Create a standalone installer for your programUnit Converter - Converts Length, Area, Volume, Weight, Temperature and Pressure to different unitsBinary Clock - Hours, minutes and seconds have 10 columns each to display timeAutoIt Editor - Code Editor with Syntax Highlighting.Laserix Editor & Player - Create, Edit and Play Laserix LevelsLyric Syncer - Create and use Synchronised Lyrics.Connect 4 - 2 Player Connect 4 Game (Local or Online!, Formatted Chat!!)MD5, SHA-1, SHA-256, Tiger and Whirlpool Hash Finder - Dictionary and Brute Force FindCool Text Client - Create Rendered ImageMy UDF's:GUI Enhance - Enhance your GUIs visually.IDEA File Encryption - Encrypt and decrypt files easily! File Rename - Rename files easilyRC4 Text Encryption - Encrypt text using the RC4 AlgorithmPrime Number - Check if a number is primeString Remove - remove lots of strings at onceProgress Bar - made easySound UDF - Play, Pause, Resume, Seek and Stop.

### #8 Daniel W.

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I hacked 127.0.0.1 !!!

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Posted 13 April 2006 - 04:13 PM

Plain Text
```\$zahl = InputBox("Zahl angeben", "Geben Sie an welche Zahl zu Ã¼berprÃ¼fen ist.")
If \$zahl = 3 Then
MsgBox(0, "", "Primzahl")
ElseIf \$zahl = 5 Then
MsgBox(0, "", "Primzahl")
ElseIf \$zahl = 7 Then
MsgBox(0, "", "Primzahl")
ElseIf \$zahl = 529 Then
MsgBox(0,"", "Keine Primzahl")
Else
\$I_Result = _MathCheckDiv(\$zahl, 2)
If \$I_Result = 2 Then
MsgBox(0,'','Keine Primzahl')
Else
\$I_Result = _MathCheckDiv(\$zahl, 3)
If \$I_Result = 2 Then
Msgbox(0, "", "Keine Primzahl")
Else
\$I_Result = _MathCheckDiv(\$zahl, 5)
If \$I_Result = 2 Then
Msgbox(0, "", "Keine Primzahl")
Else
\$I_Result = _MathCheckDiv(\$zahl, 7)
If \$I_Result = 2 Then
Msgbox(0, "", "Keine Primzahl")
Else
Msgbox(0, "", "Primzahl")
EndIf
EndIf
EndIf
EndIf
EndIf```

Hmm kk razerM and Wus
I am newbie atm so thats just the beginning of my autoIT programms maybe i get better later
Msgboxes are in German cuz i am from Germany dont wonder so ^^

Edited by Daniel W., 13 April 2006 - 04:17 PM.

--------------------------------------------------------------------------------------------------------------------------------Scripts : _Encrypt UDF_UniquePCCode UDF MS like calculatorInstall programm *UPDATED* --------------------------------------------------------------------------------------------------------------------------------

Have you ever tried surfing the internet with a milk-carton ?This is similar to what you're trying to do.

### #9 RazerM

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Posted 13 April 2006 - 04:15 PM

it doesnt work, Daniel W. You need to consider a lot more factors. try and understand what is in my script or Larry's
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### #10 Wus

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Posted 13 April 2006 - 04:16 PM

Mine should be working completly, if you find an error in it. Tell me
Msgboxes are in German cuz i am from Germany dont wonder so ^^

The problem is that your testing your input against a finite set of known primes, this cannot work since there are infinite primes. You cant use that apporach.

### #11 Confuzzled

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Posted 13 April 2006 - 06:18 PM

You code works, but the algorithm is flawed.

### #12 RazerM

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Posted 13 April 2006 - 07:26 PM

You code works, but the algorithm is flawed.

My code or Daniels code?
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### #13 greenmachine

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Posted 13 April 2006 - 11:45 PM

Mine is more along the lines of Larry's, but it does fewer because it only goes to the sqrt of the inputted number instead of half (sqrt is the correct middle). It returns an array with the prime status at [0], the first divisor at [1], and the result of the division at [2].
Plain Text
```\$prime = _checkforprime (236993)
If Not @error Then
_ArrayDisplay (\$prime, "prime")
EndIf

Func _checkforprime(\$numcheck)
Local \$divisor[3]
If Not IsInt (\$numcheck) Then
SetError (1)
Return -1
EndIf
If Mod (\$numcheck, 2) = 0 Then
\$divisor[0] = 0
\$divisor[1] = 2
\$divisor[2] = \$numcheck/2
Return \$divisor
EndIf
For \$i = 3 To Int (Sqrt (\$numcheck)) + 1 Step 2
If Mod (\$numcheck, \$i) = 0 Then
\$divisor[0] = 0
\$divisor[1] = \$i
\$divisor[2] = \$numcheck/\$i
Return \$divisor
EndIf
Next
\$divisor[0] = 1
\$divisor[1] = 1
\$divisor[2] = \$numcheck
Return \$divisor
EndFunc```

### #14 RazerM

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Posted 14 April 2006 - 05:22 PM

ive added another check to mine
Plain Text
```;===============================================================================
;
; Function Name:   _IsPrime
; Description:: Check if a number is prime or not
; Parameter(s): \$i_num - Number to check
; Requirement(s):  None
; Return Value(s): 1 - Number is prime
;                 0 - Number is not prime
;                  -1 - String isn't a number
; Author(s):       RazerM
;
;===============================================================================
;
Func _IsPrime(\$i_num)
If StringIsDigit(\$i_num) = 0 Then Return -1
If \$i_num > 3 Then
If Mod(\$i_num, 2) = 0 Then Return 0
If Mod(\$i_num, 3) = 0 Then Return 0
EndIf
If \$i_num = 1 Then Return 0
Dim \$divisor, \$increment, \$maxdivisor
\$divisor = 5
\$increment = 2
\$maxdivisor = Sqrt(\$i_num) + 1

Do
If Mod(\$i_num, \$divisor) = 0 And \$i_num <> \$divisor Then Return 0
\$divisor = \$divisor + \$increment
\$increment = 6 - \$increment
Until \$divisor > \$maxdivisor
Return 1
EndFunc ;==>_IsPrime```

Edited by RazerM, 21 April 2006 - 03:39 PM.

My Programs:AInstall - Create a standalone installer for your programUnit Converter - Converts Length, Area, Volume, Weight, Temperature and Pressure to different unitsBinary Clock - Hours, minutes and seconds have 10 columns each to display timeAutoIt Editor - Code Editor with Syntax Highlighting.Laserix Editor & Player - Create, Edit and Play Laserix LevelsLyric Syncer - Create and use Synchronised Lyrics.Connect 4 - 2 Player Connect 4 Game (Local or Online!, Formatted Chat!!)MD5, SHA-1, SHA-256, Tiger and Whirlpool Hash Finder - Dictionary and Brute Force FindCool Text Client - Create Rendered ImageMy UDF's:GUI Enhance - Enhance your GUIs visually.IDEA File Encryption - Encrypt and decrypt files easily! File Rename - Rename files easilyRC4 Text Encryption - Encrypt text using the RC4 AlgorithmPrime Number - Check if a number is primeString Remove - remove lots of strings at onceProgress Bar - made easySound UDF - Play, Pause, Resume, Seek and Stop.

### #15 GrungeRocker

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Posted 14 April 2006 - 08:16 PM

why do you need to check if a number is a prime?

EDIT1:
well i search for an old cpp example of this

EDIT2:
ok its not the same, but here you are (its in c++)
Plain Text
```#include <iostream>

using namespace std;

int main(){
int anfang, ende;
int anzprim = 0;

cin>>anfang;

cout<<"to:";
cin>>ende;

if (anfang < 2)
anfang = 2;

for (int zahl = anfang; zahl <= ende; ++zahl){
int anzteiler = 0;
int teiler = 2

while((anzteiler == 0 ) && (teiler < zahl)){
if (zahl % teiler == 0)//zahl is not a prime
anzteiler++;

teiler++;
}

if (anzteiler == 0){//zahl is a prime
cout<<zahl<<"";
anzprim++;
}
}

return 0;
}```

Edited by GrungeRocker, 14 April 2006 - 08:49 PM.

In work:

### #16 Dethredic

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Posted 17 September 2006 - 02:34 PM

I tried your script but nothing happened?!?!?

Y is this

there was no error or anything

it ran and was done in a second

Help!!!
"Its not about the 30 inch 1080p display, or the SLI 8800 ultras, or the DDR3 memory. It's about when you turn on your PC, does it return the favor?"Math is like sex. Sure, it may give some practical results, but that is not why we do it

### #17 RazerM

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Posted 17 September 2006 - 03:20 PM

If you are referring to my script then it is only a function. You need to call it like this:

`_IsPrime(\$n)`

where \$n can be any number
My Programs:AInstall - Create a standalone installer for your programUnit Converter - Converts Length, Area, Volume, Weight, Temperature and Pressure to different unitsBinary Clock - Hours, minutes and seconds have 10 columns each to display timeAutoIt Editor - Code Editor with Syntax Highlighting.Laserix Editor & Player - Create, Edit and Play Laserix LevelsLyric Syncer - Create and use Synchronised Lyrics.Connect 4 - 2 Player Connect 4 Game (Local or Online!, Formatted Chat!!)MD5, SHA-1, SHA-256, Tiger and Whirlpool Hash Finder - Dictionary and Brute Force FindCool Text Client - Create Rendered ImageMy UDF's:GUI Enhance - Enhance your GUIs visually.IDEA File Encryption - Encrypt and decrypt files easily! File Rename - Rename files easilyRC4 Text Encryption - Encrypt text using the RC4 AlgorithmPrime Number - Check if a number is primeString Remove - remove lots of strings at onceProgress Bar - made easySound UDF - Play, Pause, Resume, Seek and Stop.

### #18 jaenster

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Posted 18 September 2006 - 09:15 AM

```;Teh thing by jaenster
func omfg(\$lol)
if \$lol/2 = round(\$i/2) then
return 1
endif
return 0
endfunc```

-jaenster

### #19 Dethredic

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Posted 18 September 2006 - 02:52 PM

I have:

#include <GuiConstants.au3>

GuiCreate("Prime Finder", 316, 111,-1, -1 , BitOR(\$WS_OVERLAPPEDWINDOW, \$WS_CLIPSIBLINGS))

\$Button_1 = GuiCtrlCreateButton("Is It Prime?", 60, 60, 190, 30)
\$Input_2 = GuiCtrlCreateInput("", 10, 20, 300, 30)

GuiSetState()
While 1
\$msg = GuiGetMsg()
Select
Case \$msg = \$GUI_EVENT_CLOSE
ExitLoop
Case \$msg = \$Button_1
;read the input box here then find out if it is prime.
;if it is prime the msgbox" the number is prime
;if it isn't prime then msgbox the number is not prime
EndSelect
WEnd

how can i do this part useing your function

;read the input box here then find out if it is prime.
;if it is prime the msgbox" the number is prime
;if it isn't prime then msgbox the number is not
"Its not about the 30 inch 1080p display, or the SLI 8800 ultras, or the DDR3 memory. It's about when you turn on your PC, does it return the favor?"Math is like sex. Sure, it may give some practical results, but that is not why we do it

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Posted 18 September 2006 - 04:01 PM

Here's a funny checker: I only translated Eratosthenes function from some language to AutoIt.

AutoIt
```\$prime = Eratosthenes(50000)
For \$x = 0 to UBound(\$prime)-1
ToolTip("Now checking: " & \$x & " prime: " & \$prime[\$x], 0, 0)
If LarryPrime(\$x) <> \$prime[\$x] Then
MsgBox(0, @ScriptName, "LarryPrime is flawed, at number: " & \$x)
EndIf
If _IsPrime(\$x) <> \$prime[\$x] Then
MsgBox(0, @ScriptName, "_IsPrime is flawed, at number: " & \$x)
EndIf
Next

Func Eratosthenes(\$n)
Dim \$a[\$n+1]
For \$i = 0 to 1
\$a[\$i] = 0
Next
For \$i = 2 to \$n
\$a[\$i] = 1
Next
Dim \$p = 2
While \$p^2 < \$n+1
\$j = \$p^2
While \$j < \$n+1
\$a[\$j] = 0
\$j = \$j + \$p
WEnd
Do
\$p += 1
Until \$a[\$p] = 1
WEnd
Return \$a
EndFunc

Func LarryPrime(\$number)
Local \$DaNum
\$DaNum = Abs(\$number)
If \$DaNum < 2 And \$DaNum > -2 Then Return 1
For \$n = 2 to Int((\$DaNum/2) + 1)
If Mod(\$DaNum,\$n) = 0 Then Return 0
Next
Return 1
EndFunc

Func _IsPrime(\$i_num)
If \$i_num > 3 Then
If Mod(\$i_num, 2) = 0 Then Return 0
If Mod(\$i_num, 3) = 0 Then Return 0
EndIf
If \$i_num = 1 Then Return 0
Dim \$divisor, \$increment, \$maxdivisor
\$divisor = 5
\$increment = 2
\$maxdivisor = Sqrt(\$i_num) + 1

Do
If Mod(\$i_num, \$divisor) = 0 And \$i_num <> \$divisor Then Return 0
\$divisor = \$divisor + \$increment
\$increment = 6 - Abs(\$increment)
Until \$divisor > \$maxdivisor
Return 1
EndFunc  ;==>_IsPrime```

Edit: If someone has the CPU power and time to run it up to 100000 please do! And tell me some of the results. :)

Edited by Manadar, 18 September 2006 - 04:49 PM.

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