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prime numbers homework trouble

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Join Date: Sep 2004

Posts: 5

Reputation: bluegoo06 is an unknown quantity at this point

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bluegoo06

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prime numbers homework trouble

Mar 9th, 2005

i have to define a function that tests number from 2 to 10000 to see if they are prime.
heres what i have so far.

 Help with Code Tags 
 C++ Syntax (Toggle Plain Text) 
#include <iostream>
#include <iomanip>
using namespace std;
 
bool find_prime(int);
 
int main ()
{
	int i, counter =0;
	bool test;
 
	for (i =2; i <= 500; i++)
	{
		test = find_prime(i);
		if ( test == true )
		{
			counter++;
			cout << setw(6) << i << "\t";
		}
	}
	cout << "\nThe total number of the prime numbers between 2 and "  << i << " is " << counter << endl;
	return 0;
}
 
bool find_prime (int m)
{
 int temp, j;
 for ( j = 2; j < m - 1 ; j++ )
 {
	temp = m % j;
	if (temp == 0)
	{
	return false; 
	break;
	}
	else  
	{
	 return true;
	 break;
 }
 }}
#include <iostream>
#include <iomanip>
using namespace std;

bool find_prime(int);

int main ()
{
	int i, counter =0;
	bool test;

	for (i =2; i <= 500; i++)
	{
		test = find_prime(i);
		if ( test == true )
		{
			counter++;
			cout << setw(6) << i << "\t";
		}
	}
	cout << "\nThe total number of the prime numbers between 2 and "  << i << " is " << counter << endl;
	return 0;
}

bool find_prime (int m)
{
 int temp, j;
 for ( j = 2; j < m - 1 ; j++ )
 {
	temp = m % j;
	if (temp == 0)
	{
	return false; 
	break;
	}
	else  
	{
	 return true;
	 break;
 }
 }}

but it only tests prime numbers until about 500 or so then it gets most of the numbers to be prime but it still includes non prime numbers for some reason. ANy ideaS?
thanks

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Join Date: Apr 2004

Posts: 4,335

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Dave Sinkula Dave Sinkula is offline

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long time no c

Re: prime numbers homework trouble

Mar 9th, 2005

•

Originally Posted by bluegoo06

i have to define a function that tests number from 2 to 10000 to see if they are prime.
Help with Code Tags

(Toggle Plain Text)
for (i =2; i <= 500; i++)
for (i =2; i <= 500; i++)
but it only tests prime numbers until about 500 or so

That's what you tell it to do.

•

Originally Posted by bluegoo06

then it gets most of the numbers to be prime but it still includes non prime numbers for some reason. ANy ideaS?

You might try Google to see if there are any other algorithms to compare yours to.

"One of the methods used by statists to destroy capitalism consists in establishing controls that tie a given industry hand and foot, making it unable to solve its problems, then declaring that freedom has failed and stronger controls are necessary." --Ayn Rand

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Join Date: Feb 2005

Posts: 2

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samarth

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Re: prime numbers homework trouble

Mar 12th, 2005

Hi,

1) The "break" statement after the return does not have any effect
2) I think the logic of the program is incorrect and that may be the reason why the program returns non primes. Can u try the following code. I havent checked it but I think it should work

rgds
Sam

 Help with Code Tags 
 C++ Syntax (Toggle Plain Text) 
bool find_prime (int m)
{
 int temp, j;
 for ( j = 2; j < m - 1 ; j++ )
 {
             temp = m % j;
	if (temp == 0)
	{
	  return false; 
	}
 }
 return true;
}
bool find_prime (int m)
{
 int temp, j;
 for ( j = 2; j < m - 1 ; j++ )
 {
             temp = m % j;
	if (temp == 0)
	{
	  return false; 
	}
 }
 return true;
}