Create a program that computes all the prime numbers less than 10,000

disk97 · #1 03-Apr-2009, 01:03

Create a program that computes all the prime numbers less than 10,000 by storing them in an array and then printing them out, 10 primes to a row. (A prime is a positive integer greater than 1 whose only factors are 1 and itself).

(a)To test if a positive integer N is prime, one can divide N by all integers from 2 up to the square root of N.
As soon as you find one factor of N, you can stop.
If you get all the way to without finding a factor, then N is prime.

(b)write the program in the more efficient manner where you divide N by all primes less than or equal to , stopping if and when you find a factor.
This will require you to store the primes in an array as you compute them, and then for each integer N check to see if any elements of the array are factors of N.
This comparison will be inside a “for” or “while” loop.

c)You may enter the first element of the array, say prime[1] = 2, directly in the program.
------------------------------------------------------------------
I want to print all prime number from 2 to 10000.
10 primes to row.

my code is below

CPP / C++ / C Code:

#include <iostream>
#include<iomanip>

using namespace std;

main ()
{
	int i,j,prime[10000],count=0;

	bool flag=true;

	for (i=2;i<=10000;++i)
	{
		for (j=2;j<=sqrt(i*1.0);++j)
			if(i%j==0)
				flag=false;
		if (flag)
		{
		prime[count]=i;
		count++;
		}
	for (i=0;i<=10000;++i)    // print 10 primes to row
		{
			cout<<setw(7)<<i;
			if (i%10==9)
				cout<<endl;
		}
	}
	cout<<endl;
	cout <<"\t"<<"Program shows "<< count-1 << " all prime numbers";
	cout<<" from 2 to 10000."<<endl;
}

zalezog · #2 03-Apr-2009, 10:25

A few braces here and there and the whole program went haywire.

CPP / C++ / C Code:


for (i=2;i<=10000;++i)
	{
		 flag  = true ;//You need to assign again after 
                                   //each iteration,else will remain static           
                                   //(false)  throughout,
            //naming flag  as is_prime or something  of that sort 
           //might have been better.        
                             for (j=2;j<= (int)sqrt(i*1.0);++j) 
                                  //comparing int with a double value?,need a cast
	               {
                                   if(i%j==0)
	                    {			
                                    flag=false;
		                        break ; 
                                         //you have found one of your factors.
                                         //Why to  continue further..
                                 }
                            
                            } // j loop ends
                 
                           if (flag)
		{
		prime[count]=i;
		count++;
		}
	}  // i loop ends
                
                            for (i=0;i< count;++i)    // You have found 'count prime 
                         //numbers not  10,000
		{
			cout<<setw(7)<<i;
                //>>>While you store your prime numbers in prime[],
               //you display all the 'i' 's in the for loop,should be prime[count]
			
                                                       if (i%10==9)
				cout<<endl;
		}
	//}should be above

disk97 · #3 03-Apr-2009, 12:27

The code does not run. I fix my code but it still show one error.

Compiler error is that

Code:

Warning W8004 assign8.cpp 13: 'is_prime' is assigned a value that is never used
in function main()

The code is

CPP / C++ / C Code:


#include <iostream>
#include<iomanip>

using namespace std;

main ()
{
	int i,j,prime[10000],count=0;
	bool is_prime=true;

	for (i=2;i<=10000;++i)
	{
		is_prime=true;
		for (j=2;j<=sqrt(i*1.0);++j)
		{
			if(i%j==0)
			{
				is_prime=false;
				break;
			}
		}
		if (is_prime)
			{
			prime[count]=i;
			count++;
			}
	}
	for (i=0;i<=count;++i)    // print 10 primes to row
		{
			cout<<setw(7)<<prime[count];
			if (i%10==9)
				cout<<endl;
		}
	cout<<endl;
	cout <<"\t"<<"Program shows "<< count-1 << " all prime numbers";
	cout<<" from 2 to 10000."<<endl;
}

zalezog · #4 03-Apr-2009, 12:54

Please use code tags next time.

Please indent your code.
You also need to include

Code:


#include<cmath> //for sqrt function

Quote:

'is_prime' is assigned a value that is never used
in function main()"

I don't get this message.

disk97 · #5 03-Apr-2009, 18:16

I will use cod tags next time.
thank you very much! I got it

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search
Rate This Thread
Rate This Thread:

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Guidelines for posting requests for help - UPDATED!	WaltP	C Programming Language	1	11-Nov-2007 22:05
Barcode reader code problem	copa_21	C Programming Language	5	13-Oct-2006 01:40
User defined headers	davis	Miscellaneous Programming Forum	6	16-Feb-2006 19:40
Could Someone Please Explain This Code To Me	HelpMePlease	C Programming Language	3	26-May-2004 23:46
something wrong with this code	loon	MySQL / PHP Forum	5	07-Jul-2003 06:55

Create a program that computes all the prime numbers less than 10,000

Re: Create a program that computes all the prime numbers less than 10,000

Re: Create a program that computes all the prime numbers less than 10,000

Re: Create a program that computes all the prime numbers less than 10,000

Re: Create a program that computes all the prime numbers less than 10,000