筛法求素数

using System;
public class PrimeFilter
{
    public static void Main( string [] args )
    {
        int N = 100;
        bool [] a = new bool[N+1];//bool数组

        for( int i=2; i<=N; i++ ) 
            a[i]=true;

        for( int i=2; i<N; i++ )
        {
            if(a[i]){
                for( int j=i*2; j<=N; j+=i )
                    a[j]=false;
            }            
        }

        for( int i=2; i<=N; i++) 
            if( a[i] ) Console.Write( i + " " );

        Console.ReadLine();//暂停
    }
}