Please Ignore
[79 byte] By [Overkilla] at [2007-11-27 8:39:51] 
NVM I figured it out.. doh!Message was edited by: Overkill
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Ok, I'm not going to look at your code: you should really split things into two separate methods. Here's some pseudo code:
public class TwinPrimes {
public void displayTwinPrimes(int low, int high) {
/*
LOOP 'i' from 'low' to 'high'
IF 'i' is a prime
IF 'i' is even
print '2,3'
ELSE IF 'i'+2 is prime
print 'i' and 'i'+2
END IF
END IF
END LOOP
*/
}
public boolean isPrime(int n) {
// return true iff 'n' is prime
}
public static void main(String[] args) {
new TwinPrimes().displayTwinPrimes(1,100);
}
}
Message was edited by:
prometheuzz
Although you figured it out, I suggest rewriting your application as I suggested: the sooner you learn yourself to split multiple responsibilities into their own methods, the better!
prometheuzza at 2007-7-12 20:38:01 >
Its good you posted that , since right now ive come up with this code, which only prints 1,3
Im taking a look at your code, and after understanding it will write it properly. Thanks
public class TwinPrimeNum//Calculate twin primes from 1-100
{
private int a,b;
public void calculate()
{
for (int i=1;i<=100;i++)
{
for (int j=1;j<=i;j++)
{
if (i%j==0)
{
a++;
}
if ((i+2)%j==0)
{
b++;
}
}
if (a<=2 && b<=2)
System.out.print(i+","+(i+2));
}
}
}
Overkilla at 2007-7-12 20:38:01 >
So i finished translating your pseudo code into BlueJ code(and I removed the low and high things, made it so its only 1 to 100), and it works in a very weird way .. the output it somewhat correct...
This is the output:
1,12
2,3
3,32
5,52
11,112
17,172
29,292
41,412
59,592
71,712
and Twin primes upto 100 are :
(3, 5), (5, 7), (11, 13), (17, 19), (29, 31), (41, 43), (59, 61), (71, 73), (101, 103)
and this is the code
public class TwinPrimeNumber
{
private int a;
public void display()
{
for (int i=1;i<=100;i++)
{
if (isPrime(i)==true)
{
if (i%2==0) System.out.println("2,3");
else if (isPrime(i+2)==true)
{
System.out.println(i+","+i+2);
}
}
}
}
public boolean isPrime(int n)
{
a=0;
for (int i=1;i<=n;i++)
{
if (n%i==0)
a++;
}
if (a<=2)
return true;
else
return false;
}
}
BTW i added a=0 at the top of the isPrime method coz otherwise after the first number , a will always be greater than 2 and nothing will be prime
Message was edited by:
Overkill
Overkilla at 2007-7-12 20:38:01 >
> So i finished translating your pseudo code into BlueJ
> code(and I removed the low and high things, made it
> so its only 1 to 100), and it works in a very weird
> way .. the output it somewhat correct...
Almost!
Instead of doing:
System.out.println(i+","+i+2);
do it like this
System.out.println(i+","+(i+2));
And the number one is not a prime number.
prometheuzza at 2007-7-12 20:38:01 >
Woah!
**** so the +i+2 was making the second + act like a concatenation operator instead of adding...
dooh!
Cool man thanks not only for this program but for introducing me to the basic concept of Object Oriented Programming(using seperate methods IS oop right?). It makes the code so much easier to understand.
Overkilla at 2007-7-12 20:38:01 >
> Woah!
> **** so the +i+2 was making the second + act like a
> concatenation operator instead of adding...
> dooh!
Yeah, that's a classic one.
; )
> Cool man thanks not only for this program but for
> introducing me to the basic concept of Object
> Oriented Programming(using seperate methods IS oop
> right?). It makes the code so much easier to
> understand.
Correct, that's (a part of) OO programming indeed.
Just one small remark about you current isPrime(...) method:-
- that int a should be only visible inside your isPrime(...) method;
- you need not check a number n up to itself for primality: up to the square root is sufficient. If you want to check if 31 is a prime, you can stop the loop when you have reached 6;
So, here's some pseudo code for the isPrime(...) method:
public boolean isPrime(int n) {
/*
IF 'n' is less than 2
'n' is no prime, return false
ELSE IF 'n' equals 2
'n' is prime, return true
END IF
'max' <- (square root of 'n') + 1
FOR 'i' = 2 to 'max'
IF 'i' divides 'n'
'n' is no prime, return false
END IF
END FOR
'n' must be prime if we get here, return true
*/
}
Now you can go ahead with your prime-research and wrap up your proof that there are an infinite number of twin primes... Or aren't there?
; )
prometheuzza at 2007-7-12 20:38:01 >
> Now you can go ahead with your prime-research and
> wrap up your proof that there are an infinite number
> of twin primes... Or aren't there?
> ; )
And when you're done with that, you can move on to these:
http://en.wikipedia.org/wiki/Hilbert%27s_problems
petes1234a at 2007-7-12 20:38:01 >
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