## VB.NET

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Number of posts: 10026

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prime numbers Posted by hsnester on 27 Sept 2006 at 7:52 PM
hey i learnd vb 2 years ago and i kinda forgot how to use it but im trying to make a program that creates all the prime numbers up to 1000 so if anyone has any help or ideas on what to do it would be great

Re: prime numbers Posted by PavlinII on 28 Sept 2006 at 6:27 AM
: hey i learnd vb 2 years ago and i kinda forgot how to use it but im trying to make a program that creates all the prime numbers up to 1000 so if anyone has any help or ideas on what to do it would be great
:
:
Hi,
how sophisticated is your algorithm supposed to be?
The easiest (and stupidest) way could look like this:
```Dim Primes As String = Nothing
For i As Integer = 1 To 1000
If IsPrime(i) Then Primes &= i & ", "
Next
MsgBox(Primes)

...

Private Function IsPrime(ByVal N As Integer) As Boolean
For i As Integer = 2 To N - 1
If N Mod i = 0 Then Return False
Next
Return True
End Function```
This has asymptotic complexity N*N but who cares with N=1000..
You can make few optimalisations here (to divide by only previously found prime numbers to decrease number of dividing etc), or other more complicated algorithms up to Eucleid's one..

Pavlin II[/size]

Don't take life too seriously anyway you won't escape alive from it!

Re: prime numbers Posted by hsnester on 28 Sept 2006 at 10:11 AM
: : hey i learnd vb 2 years ago and i kinda forgot how to use it but im trying to make a program that creates all the prime numbers up to 1000 so if anyone has any help or ideas on what to do it would be great
: :
: :
: Hi,
: how sophisticated is your algorithm supposed to be?
: The easiest (and stupidest) way could look like this:
:
```Dim Primes As String = Nothing
:   For i As Integer = 1 To 1000
:     If IsPrime(i) Then Primes &= i & ", "
:   Next
:   MsgBox(Primes)
:
: ...
:
:   Private Function IsPrime(ByVal N As Integer) As Boolean
:     For i As Integer = 2 To N - 1
:       If N Mod i = 0 Then Return False
:     Next
:     Return True
:   End Function```
This has asymptotic complexity N*N but who cares with N=1000..
: You can make few optimalisations here (to divide by only previously found prime numbers to decrease number of dividing etc), or other more complicated algorithms up to Eucleid's one..
:
: Pavlin II[/size]
:
: Don't take life too seriously anyway you won't escape alive from it!
:
:
: hey thanks man lol you had the one piece i was missing. you saved my grade haha

Re: prime numbers. Code amended a tiny bit. :-) Posted by DrMarten on 28 Sept 2006 at 1:00 PM
This message was edited by DrMarten at 2006-9-28 13:1:14

: : hey i learnd vb 2 years ago and i kinda forgot how to use it but im trying to make a program that creates all the prime numbers up to 1000 so if anyone has any help or ideas on what to do it would be great
: :
: :
: Hi,
: how sophisticated is your algorithm supposed to be?
: The easiest (and stupidest) way could look like this:
```Dim Primes As String = Nothing
'Step 2 added as a PRIME can only be an odd number.
For i As Integer = 1 To 1000 Step 2
If IsPrime(i) Then Primes &= i & ", "
Next
MsgBox(Primes)

Private Function IsPrime(ByVal N As Integer) As Boolean

For i As Integer = 2 To N - 1
If N Mod i = 0 Then Return False
Next

Return True

End Function
```

This has asymptotic complexity N*N but who cares with N=1000..
: You can make few optimalisations here (to divide by only previously found prime numbers to decrease number of dividing etc), or other more complicated algorithms up to Eucleid's one..
:
: Pavlin II[/size]

: Don't take life too seriously anyway you won't escape alive from it!

Step 2 would speed things up a bit if you went up to say 100,000.

There are other rules to find a PRIME number of course.
Simpler ones include;

i) It has to be an odd number.
ii) Any number ending in a five doesn't count.
iii) If you add all the digits are added and the result divides by 9 like in the number.>>

123456789 like 1+2+3+4+5+6+7+8+9=45 >> 4+5=9

Then as 45 is 5 times 9 then the bigger number divides exactly by 9.

This rule works for any number of any length!!

So this rule is obviously true for the number.>>

112233445566778899

And the numbers in the next applicable date of;

09-10-2006 ( 9th Oct,2006 ).

Regards,

Dr M.

Re: prime numbers. Code amended a tiny bit. :-) Posted by hsnester on 28 Sept 2006 at 1:12 PM
: This message was edited by DrMarten at 2006-9-28 13:1:14

: : : hey i learnd vb 2 years ago and i kinda forgot how to use it but im trying to make a program that creates all the prime numbers up to 1000 so if anyone has any help or ideas on what to do it would be great
: : :
: : :
: : Hi,
: : how sophisticated is your algorithm supposed to be?
: : The easiest (and stupidest) way could look like this:
:
```Dim Primes As String = Nothing
:  'Step 2 added as a PRIME can only be an odd number.
:  For i As Integer = 1 To 1000 Step 2
:     If IsPrime(i) Then Primes &= i & ", "
:  Next
:  MsgBox(Primes)
:
: Private Function IsPrime(ByVal N As Integer) As Boolean
:
:  For i As Integer = 2 To N - 1
:     If N Mod i = 0 Then Return False
:  Next
:
:  Return True
:
: End Function
: ```

: This has asymptotic complexity N*N but who cares with N=1000..
: : You can make few optimalisations here (to divide by only previously found prime numbers to decrease number of dividing etc), or other more complicated algorithms up to Eucleid's one..
: :
: : Pavlin II[/size]
:
: : Don't take life too seriously anyway you won't escape alive from it!
:
: Step 2 would speed things up a bit if you went up to say 100,000.
:

:
: There are other rules to find a PRIME number of course.
: Simpler ones include;
:
: i) It has to be an odd number.
: ii) Any number ending in a five doesn't count.
: iii) If you add all the digits are added and the result divides by 9 like in the number.>>
:
: 123456789 like 1+2+3+4+5+6+7+8+9=45 >> 4+5=9
:
: Then as 45 is 5 times 9 then the bigger number divides exactly by 9.
:
: This rule works for any number of any length!!
:
: So this rule is obviously true for the number.>>
:
: 112233445566778899
:
: And the numbers in the next applicable date of;
:
: 09-10-2006 ( 9th Oct,2006 ).
:
:
: Regards,
:
: Dr M.
:
:
haha thanks youv really been a help right now im working on this one project that is pretty fun but really had to do. its a program that generates all the vampire numbers(a vampire number is a two two digit number that equal a four digit number and all the numbers in the two two digit numbers have to be in that four digit number)i mean im sure you could do it but dont be supprised if later on i come to you asking for advice lol and again thanks youv been a great help

sencerly

2nd LT. Nester
Re: Vampire numbers. [AMENDED]. Posted by DrMarten on 28 Sept 2006 at 2:10 PM
This message was edited by DrMarten at 2006-9-28 14:54:33

: : : : hey i learnd vb 2 years ago and i kinda forgot how to use it but im trying to make a program that creates all the prime numbers up to 1000 so if anyone has any help or ideas on what to do it would be great
: : : :
: : : :
: : : Hi,
: : : how sophisticated is your algorithm supposed to be?
: : : The easiest (and stupidest) way could look like this:
: :
```Dim Primes As String = Nothing
: :  'Step 2 added as a PRIME can only be an odd number.
: :  For i As Integer = 1 To 1000 Step 2
: :     If IsPrime(i) Then Primes &= i & ", "
: :  Next
: :  MsgBox(Primes)
: :
: : Private Function IsPrime(ByVal N As Integer) As Boolean
: :
: :  For i As Integer = 2 To N - 1
: :     If N Mod i = 0 Then Return False
: :  Next
: :
: :  Return True
: :
: : End Function
: : ```

: : This has asymptotic complexity N*N but who cares with N=1000..
: : : You can make few optimalisations here (to divide by only previously found prime numbers to decrease number of dividing etc), or other more complicated algorithms up to Eucleid's one..
: : :
: : : Pavlin II[/size]
: :
: : : Don't take life too seriously anyway you won't escape alive from it!
: :
: : Step 2 would speed things up a bit if you went up to say 100,000.
: :

: :
: : There are other rules to find a PRIME number of course.
: : Simpler ones include;
: :
: : i) It has to be an odd number.
: : ii) Any number ending in a five doesn't count.
: : iii) If you add all the digits are added and the result divides by 9 like in the number.>>
: :
: : 123456789 like 1+2+3+4+5+6+7+8+9=45 >> 4+5=9
: :
: : Then as 45 is 5 times 9 then the bigger number divides exactly by 9.
: :
: : This rule works for any number of any length!!
: :
: : So this rule is obviously true for the number.>>
: :
: : 112233445566778899
: :
: : And the numbers in the next applicable date of;
: :
: : 09-10-2006 ( 9th Oct,2006 ).
: :
: :
: : Regards,
: :
: : Dr M.
: :
: :
: haha thanks youv really been a help right now im working on this one project that is pretty fun but really had to do. its a program that generates all the vampire numbers(a vampire number is a two two digit number that equal a four digit number and all the numbers in the two two digit numbers have to be in that four digit number)i mean im sure you could do it but dont be supprised if later on i come to you asking for advice lol and again thanks youv been a great help
:
: sencerly
:
: 2nd LT. Nester

====================================================================

Hi do you mean like 12 and 34 giving.>>

1234 or
1243 or
1324 or
1342 or
2134 or
2143 or
2314 or
2341 or

and the remaining 8 numbers?

In which case there will always be 16 results.
They are PERMUTATIONS.

abc giving

ab
ac
bc
with one function which is COMBINATION (3 C 2)

ab, ba
ac, ca
bc, ca

when you take 2 letter permutations (3 P 2) from the 1st three letters.
http://mathforum.org/dr.math/faq/faq.comb.perm.html

and the following two pages for formulas involving factorials> :-|

http://www.mathwords.com/p/permutation_formula.htm
where order matters, see.>>
http://www.mathwords.com/p/permutation.htm

http://www.mathwords.com/c/combination_formula.htm
where order doesn't matter see.>>
http://www.mathwords.com/c/combination.htm

Regards,

Dr M.

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