math problems

[TokenHerbz]

I want to make a code that asks the user for 2 numbers, and inbetween these numbers it will print out numbers which are only able to divide by its self, and 1 evenly...

Ex, 1,2,3,5,7,11 ( i think )

code:

var num1, num2: int var n1, n2: int put "please enter 1 number" get num1 put "please enter another number" get num2 if num1 < num2 then     n1 := num1     n2 := num2 elsif num1 > num2 then     n1 := num2     n2 := num1 else     put "Bah, your numbers are the same" end if for i: 1 .. n2     if i >= n1 then         if i / i = 1 then     %%% <--   heres where i need the math help?             put i         end if     end if end for

Help me please

[zylum]

so you want to print the primes in a range of numbers?

code:

var a, b : int put "what are the numbers" get a, b var primes : array 1 .. b of boolean for i : 1 .. b     primes (i) := true end for for i : 2 .. b     for j : i * 2 .. b by i         primes (j) := false     end for end for for i : 1 .. b     if primes (i) then         put i, " ", primes (i)     end if end for

[Drakain Zeil]

I ran through a for loop with i as a count.

if i was not divisable by the number,(use mod), then I would output.

You only need to run the loop from: a..(b/2)+1
And a decent range for prime check is (a/3)-1..(b/2)+1

[GlobeTrotter]

Drakain Zeil wrote:

I ran through a for loop with i as a count.

if i was not divisable by the number,(use mod), then I would output.

You only need to run the loop from: a..(b/2)+1
And a decent range for prime check is (a/3)-1..(b/2)+1

Actually to check for a given prime, you only need to check if the number is divisible by any prime between 0 and the root of the number.

[jamonathin]

Drakain Zeil wrote:

Actually to check for a given prime, you only need to check if the number is divisible by any prime between 0 and the root of the number.

But if we're looking for a prime number, how would be divide it by primes to find out if it's prime?

[Cervantes]

jamonathin wrote:

But if we're looking for a prime number, how would be divide it by primes to find out if it's prime?

Start from the bottom up.