循环语句举例

public class JCH {

    public static void main(String[] args) {
        
        //数组
        int[] a = new int[3];
        a[0] = 1;
        a[1] = 2;
        a[2] = 3;
        //a[3] = 4;最大就是长度减一，超出运行报错（从0开始）
        int len = a.length;//获取数组成都
        
        System.out.println("数组的长度 =" + len);
        for(int i=0;i< a.length;i++)
            System.out.println("a["+i+"]=" + a[i]);
        
        System.out.println("a[0]=" + a[0]);
        int b[];
        
        
        
        
        
        
        
        
        // 用循环实现阶乘
        int n = 12;
        
        //4!=1*2*3*4=24
        
        long l = 1;//阶乘计算结果
        
        
        for(int i = 1;i <= n; i ++){
            
            
            l =l * i ;
            
            System.out.println("l =" + l);
            
        }
            System.out.println(n + "!=" + l );    
            
            //1+1/2!+1/3!+.....+1/20!=?
            
            
            int y = 20;
            
            double d = 0;
            for(int k = 1;k <= y;k++)
            {
                long s = 1;
                for(int i = 1;i <= k; i ++){
            //计算阶乘 k!
                    s =s * i ;
                    
                    System.out.println(s + "!=" + s);
                }
                 d = d + 1/(double)s;
                
            }
            System.out.println("1/"+ y +"!=" + d);
            
            
            
            
            //循环嵌套  花三角形
            
            int m = 10;   //行数
            
            for(int i = 1;i <= m;i++){
                
                for(int j = 1;j <= i;j++){
                    
                    System.out.print("*");
                }
                System.out.println();
                
                
            }
            
            
            
            
            for(int i = m;i >= 1;i--)
            {
                for(int j = 1;j <= i;j++)
                {
                    System.out.print("*");
                }
                System.out.println();
            }
            
            
            
            /*    for(int i = m - 1;i >= 1;i--){
                    
                    for(int j = 1;j <= i;j++){
                        
                        System.out.print("*");
                    }
                    System.out.println();
                
            }*/

    }

}