java基础 java流程控制

Switch case 循环

输入年和月，输出该年和该月有多少天？

 
    public static void main(String[] args) {
        System.out.println("请输入年");
        Scanner sc1 = new Scanner(System.in);
        int year = sc1.nextInt();
        System.out.println("请输入月");
        int month = sc1.nextInt();
        //逻辑
        switch (month){
            case 1:
            case 3:
            case 5:
            case 7:
            case 8:
            case 10:
            case 12:
                System.out.println("该月有31天");
                break;
            case 4:
            case 6:
            case 9:
            case 11:
                System.out.println("该月有30天");
                break;
            case 2:
                //闰年的条件  能被400整除   或者  能被4整除并且不能被100整除
                if (year%400==0 || year%4==0 && year%100!=0){
                    System.out.println("该月有29天");
                }else{
                    System.out.println("该月有28天");
                }
                break;
            default:
                System.out.println("输入数据不合法");
                break;
        }

for循环输出九九乘法表和反向九九乘法表

 for (int i = 1; i < 10; i++) {
            for (int j = 1; j <= i; j++) {
                System.out.print(j+"*"+i+"="+i*j+" ");
            }
            System.out.println();
        }
        System.out.println("---------------------------------");
        for (int i = 9; i >=1; i--) {
            for (int j = 1; j <=i; j++) {
                System.out.print(j+"*"+i+"="+i*j+" ");
            }
            System.out.println();
        }
        System.out.println("---------------------------------");
        for (int i = 1; i < 10; i++) {
            for (int j = 9; j >=i; j--) {
                System.out.print(j+"*"+i+"="+i*j+" ");
            }
            System.out.println();
        }

        System.out.println("---------------------------------");
        for (int i = 9; i >=1; i--) {
            for (int j = 9; j >= i; j--) {
                System.out.print(j+"*"+i+"="+i*j+" ");
            }
            System.out.println();
        }

循环录入五次成绩，求和  求平均值  求最大值  求最小值。

 double sum = 0;
        double max = 0;
        double min = 0;
        for (int i = 1; i <= 5; i++) {
            System.out.println("请输入第"+i+"次成绩");
            Scanner sc = new Scanner(System.in);
            double score = sc.nextDouble();
            sum+=score;
            //假设：默认第一个输入的数既是最大值 也是最小值   比武招亲打擂台
            if(i==1){
                max = score;
                min = score;
            }
            if(max < score){
                max = score;
            }
            if(min > score){
                min = score;
            }
        }
        System.out.println("和是"+sum+",平均值是"+sum/5+",最大值："+max+";最小值："+min);

输出所有5位数中的回文数

 鸡兔同笼：总共100个脚，各多少只 ？

计算sum=1-1/2+1/3-1/4+1/5-……+1/99的值。

//计算sum=1/1-1/2+1/3-1/4+1/5-……+1/99-1/100的值。
        //sum = 1 - (1/2+...+1/100) + (1/3+...+1/99);
        //方法一
        

		//方法二
        

		//方法三
        double a = 0;
        double b = -1;
        for (double i = 1; i <=100; i++) {
            b = b*(-1);
            a += b*(1/i);
        }
        System.out.println(a);