[kavi]

I need help!!

I Can not invent the algorithm of this programm. Can someone help me?

input number "n" and the programm shows all prime number who is lesser than number "n" and whom can enounce like 2^k -1

This post has been edited by kavi: 03 November 2006 - 11:38 AM

[Jayman]

Post the code you have completed so far and someone will be happy to help you.

[kavi]

#include <iostream>
int x (int n,int m); //deklaree visus mainiigos
using namespace std;

int main()
{
	int n, m=0;
	char exit;
	do
	{
		 cout << "\nInput number, \nthe programm will show \nall prime number who is \nlesserthan your input number \nand which can enounce like 2^k -1 ";
		 cin  >> n;
		 cout << "\nYour input number is : "  << n << endl; 
		 
		 ................................. <<< I can`t  invent what be writen in here
		 
		 cout << "\nPrime number wich is lesser than your nummber and \nwich enounce like 2^k -1 is  : "  << m << endl;
		 cout << "\nRepeat the programm <y/n> " << endl;
		 cin  >> exit;
	}
while (exit=='y');

return 0;
}

[dorknexus]

a prime number is a number which is divisible only by itself and one

thus the following algorithm, should verify whether a number is prime or not

bool isPrime(int num)
{
	 for (int i = 2;i < num;++i)
	 {
		  if (num % i == 0)
			   return false;
	 }

	 return true;
}

[born2c0de]

Quote

a prime number is a number which is divisible only by itself and one

or you can write the function using the exact definition that Dark_Nexus gave:

int isprime(int x)
{
   int i=2;
   while(x%i)i++;

   return (x==i);
}