筛法求素数

 1 using System;
 2 public class PrimeFilter
 3 {
 4     public static void Main( string [] args )
 5     {
 6         int N = 100;
 7         bool [] a = new bool[N+1];//bool数组
 8 
 9         for( int i=2; i<=N; i++ ) 
10             a[i]=true;
11 
12         for( int i=2; i<N; i++ )
13         {
14             if(a[i]){
15                 for( int j=i*2; j<=N; j+=i )
16                     a[j]=false;
17             }            
18         }
19 
20         for( int i=2; i<=N; i++) 
21             if( a[i] ) Console.Write( i + " " );
22 
23         Console.ReadLine();//暂停
24     }
25 }