a special function listing all the factors of an integer

[Tricia]

is there any special function or command or statement for that?

[Paul]

I don't think so... I think you'll have to find out the factors normally through running a loop to that number... Um I'm rusty, but I'll try:

code:

var num: int put "Input integer: ".. get num for a: 1..num %runs loop from 1 to the integer if strintok(realstr(num/a,0)) then %checks if num/a is integer or not %so if u enter 5, 5/1 = 5, thats a factor, 5/2 is 2.5, which is not %an integer, so not factor. put a, " ".. end if end for

there's prolly lots of stuff I didn't think of, but its too late, can't think.

[wtd]

First, we'll define a function to determine if a number is prime. Prime numbers are divisible only by themselves and one.

To find if a number is prime, we'll count up from two to one less than the original number. If the number is evenly divisible by any of these, then it can't be prime. If it goes all the way through without this happening, we know the number is prime.

code:

function prime(n : int) : boolean    for c : 2 .. (n - 1)       if (n mod c) = 0 then          result false       end if    end for    result true end prime

We can now use this function to make sure the factors we find are prime.

Now, we'll create a function which finds the smallest factor of a given number.

First we check to see if the number is a prime number. If it is, then we can't factor it, and there's no point trying. We can just return that number.

If it's not a prime, we'll again count up, and as soon as we find a factor, we'll return that. We will find a factor before the end of the loop.

code:

function findSmallestFactor(n : int) : int    if prime(n) then       result n    else       for c : 2 .. (n - 1)          if (n mod c) = 0 then             result c          end if       end for    end if      end findSmallestFactor

Now, to put it all together. We'll start out with a number. We have a loop. Each time around we find the smallest factor of that number. If the smallest factor is the number, then we exit the loop. Otherwise we print the smallest factor, divide the number by the factor we found and start the loop all over.

code:

procedure printFactors(var n : int)    loop       var smallestFactor : int := findSmallestFactor(n)             if smallestFactor = n then          exit       else          put smallestFactor          n /= smallestFactor          % equivalent to:          % n := n / smallestFactor       end if    end loop end printFactors

Any questions?

[Paul]

uh... so I was wrong then?

[wtd]

I can't test it to see if it works. However, I prefer to use math. Munging things back and forth from numbers to strings just feels wrong if it can be done another way.

[Cervantes]

Pauls works, its just a little indirect.
instead of using strintok and realstr and such you could just use mod

code:

var num : int put "Input integer: " .. get num for i : 1 .. num     if num mod i = 0 then         put i, "  " ..     end if end for

[wtd]

Cervantes wrote:

Pauls works, its just a little indirect.
instead of using strintok and realstr and such you could just use mod

code:

var num : int put "Input integer: " .. get num for i : 1 .. num     if num mod i = 0 then         put i, "  " ..     end if end for

The only problem with this approach is that you won't get prime factors of an integer. Say you start with 64. You'll get:

1
2
4
8
16
32
64

Only two of those numbers are primes, and 1 and 64 can be elided since 1 and itself are always factors of a number.

[Paul]

well... he asked for factors, I never thought about prime factors.

[wtd]

What can I say... I am (or at least was) a math geek.