Checking for all divisible factor of a number

[aznrex]

Hey,
one of my work question is telling me to make a program where the user will input an Int number and check whether it is a perfect number or not
for those who dont know what a perfect number is :
a perfect number, is a number where the sum of all its dividable factors other then it self is equal to the number it self ie:
1 + 2 + 3 = 6
1 2 and 3 are int number that 6 can evenly divid into, and the sum is also 6

1 + 2 + 4 + 7 + 14 = 28
1 2 4 7 14, are int number that 28 can evenly divid into, and the sum will be 28

ok,
so my problem is whether it is possoble for turing to find out all the dividable factors thats an int, of a number. also how it shows it to the user

thanks

[MysticVegeta]

Wasnt this a DWITE Contest problem? Anyways, We cant "do" it for you but I can help you with the pseudocode :

Ok think about this, you need a variable that stores the sum of factors. Now, You need to check whether a number is divisible by the main number. So you need a "for" loop for that. Make sure you understand the "mod" function. Press F10, and check that out. In the end, check if the sum > num or < num or = num.

[aznrex]

hmm,
i dont think you would mod this number
because i need the actualy value when i divid, say "a" by the counter
also, is it possbible for when u divid a/counter (from for counter : 1 .. a)
and only divid whole numbers?? and not any decimals
then somehow store the sum of all those whole number and check whether it is equal to "a"

[GlobeTrotter]

Try this code for the first couple of perfect numbers.

code:

fcn isPrime (n : int) : boolean     if n = 2 then         result true     end if     for i : 2 .. n - 1         if n mod i = 0 then             result false         end if     end for     result true end isPrime for n : 2 .. 13     if isPrime ((2 ** n) - 1) then         put ((2 ** n) - 1) * (2 ** (n - 1))     end if end for

[aznrex]

hmm, can you please explain to me what is happening in teh code??
ie what is fcn?

[aznrex]

actually,
what does n repersent and what does i repersent??
i get your logic of the code

[Cervantes]

aznrex wrote:

hmm, can you please explain to me what is happening in teh code??
ie what is fcn?

fcn stands for function. To learn about functions, check out our tutorial on the subject, which can be found in [Turing Tutorials]. There's a link to it in the Turing Walkthrough, as well.

In terms of the isPrime function, n represents the number in question. Is n a prime number? That's what the function determines. i is used to iterate through various numbers, checking whether they are a factor of n.

GlobeTrotter: Why don't you use the following?

code:

for i : 2 .. n div 2

[GlobeTrotter]

Cervantes wrote:

GlobeTrotter: Why don't you use the following?

code:

for i : 2 .. n div 2

I could have made the isPrime function more efficient. Actually rather than going up to n div 2, I could have gone up to ceil(sqrt(n)). Anything above that would be redundant.

[aznrex]

hmm, but i am trying to write a program to check for a perfect number not generate,

what i was thinking is whether turing has any fucntion that will only display or store numbers that are whole ( like 1, 2 , 3 and not 1.1 or 2.4 etc)

after the number is stored, say var a then i can go like n (user inputed number) and do this : if n = a - n then
put "it is perfect number"
sumthing like this, but so far i am not able to do that

[person]

code:

for x : 1 .. a - 1     if a mod x = 0 then         b += x     end if end for

[MysticVegeta]

Wrong way to code Xiao, If n is a huge number, execution takes forever, I think GlobeTrotter's method is better, its faster.

Btw you can "for x : 1..ceil(n/2) " too saving more time