package arrays;

import java.io.*;

public class PrimeSieve {
    // This program implements the Sieve of Eratosthenes

    public static void main (String args []) 
        throws Exception {

    // declare basic objects
        InputStreamReader istream  = new InputStreamReader(System.in);
        BufferedReader in = new BufferedReader(istream);
        PrintWriter out = new PrintWriter(System.out, true);
        int M;           // size of sieve
        int i, number;   // indices
        String line;     // use to read a line

        // Determine size of sieve
        out.println ("Use of the Sieve of Eratosthenes to compute primes");
        out.println ("Enter how large an integer to process:  ");
        line = in.readLine();
        M = new Integer(line).intValue();
        
        // set up sieve
        boolean [] crossedOut = new boolean [M+1]; 
        // use size M+1 for elemens 0 through M
        for (i = 0; i<= M; i++)  // i++ is an abbreviation for i = i + 1
            crossedOut[i] = false;
        
        // follow cross-out process
        for (number = 2; number < M; number++)
            {if (!crossedOut[number])
                { // cross out multiples of number
                    i = 2*number;
                    while (i <= M) 
                        { crossedOut[i] = true;
                        i = i + number;
                        }
                }
            }

        // print list of primes
        out.println ("The following prime numbers have been found");
        int numberOnLine = 0;

        for (i = 2; i <= M; i++)
            {if (!crossedOut[i])
                {
                    out.print(i + "\t");  // add tab after each number
                    numberOnLine++;
                    if (numberOnLine == 8)
                        {
                            out.println(); // start a new line every 8 numbers
                            numberOnLine = 0;
                        }
                }
            }
        out.println();
    }
}