for loop query

[sedy]

hi, I am writing prime number program using labview.I wrote the same with matlab as below

N=input('enter number ');

prime=[];

for j=3:N;

M=ceil(j/2);

for i =2:M;

k = mod(j,i);

if k==0

   break;

end

if i==M

  prime=[prime j];

end

end

end

prime=[2 prime];

Now ,in labview i hv 2 questions

1)how i implement for loop which starts at say 3 and ends at say N=20

2)how do i manipulate loop variable?

any help will be highly appreciated

thnks

sedy 

[altenbach]

---

sedy wrote:

Now ,in labview i hv 2 questions

1)how i implement for loop which starts at say 3 and ends at say N=20

2)how do i manipulate loop variable?

---

(1) Well, you just calculate the number of iterations and then increment the iteration terminal by the start value, e.g. as follows:

(2) Sorry, I don't quite understand what kind of "manipulations" you have in mind.

You might also want to look at the prime factor challenge discussion. It shows a few algorithms to generate prime factors a bit more efficiently.

Message Edited by altenbach on 01-17-2009 01:06 AM

[Pnt]

If you need a variable for the loop, use a shift register.

Right click on the border of the loop and select add shift register.

[sedy]

hi,

thnks.

let me try first. 

[sedy]

hi,

ok,let me try.

thnks 

[sedy]

hi,

I have done that and even i m getting prime numbers as variable say j. now,the problem is,this variable is inside 2  for loops,

so when i want to make array out of it, i simply updates value at same location.e.g for prime numbers between 2 to 10, it updates value 7(last prime

number) at same loaction instaed of displaying 2,3,5,7. i tried with bulid array,insert array,no use, they update at same location.

so, how can i make array in which elemnts add automatically at contigous locations? 

[Zinnium]

---

hi,

I have done that and even i m getting prime numbers as variable say j. now,the problem is,this variable is inside 2  for loops,

so when i want to make array out of it, i simply updates value at same location.e.g for prime numbers between 2 to 10, it updates value 7(last prime

number) at same loaction instaed of displaying 2,3,5,7. i tried with bulid array,insert array,no use, they update at same location.

so, how can i make array in which elemnts add automatically at contigous locations?

---

Inside the "for loop" you can add an "if statement" or "while loop" inside the "for loop" to do this.  Code it so that they will kill when a prime number is found and or when the range is meet, and you get your output just the way you want it.   I had to do something simlar in a class a long time ago and I found a "for" and "while" loop combination worked the best.

 I thought there was a prime number function already built into labview or it may have been a custom library you could download???  I do remember it, and being angery I had to do all that work in class.

Zi

[altenbach]

For illustration, here's a "near literal" translation of your code into LabVIEW with some annotations. See if it makes sense. 😉

(There are a couple of problems with your algorithm, for example if N=1 or 0, primes = [2], because the "2" is prepended without thinking ;))

Of course, as I mentioned before, there are much (much!!!) faster and more efficient algorithms for all this 😄

.... However, for learning about FOR loops, this is fine. See of you find any bugs 😉

Message Edited by altenbach on 01-17-2009 01:21 PM

[sedy]

hi alten,

well,I had made the program almost 90% similar to wht u hv shown. and for N=0,N=1, i was not that much bothered.so,let me c,if the array portion i can work out.

thnks so much,i cant beleive people can spare time to make program out of my code..i really am thankful.

sedy