Java学习 5.习题2.

        int num1=10;
        if(num1%2==0) {
            System.out.println("num1是一个偶数");
        }else{
            System.out.println("num1是一个奇数");
        }

        int num2=-5;
        if(num2>0) {
            System.out.println("num2是正数");
        }else if(num2==0){
            System.out.println("num2是0");
        }else{
            System.out.println("num2是负数");
        }

        System.out.println("请输入一个年份");
        Scanner sc1=new Scanner(System.in);
        int year=sc1.nextInt();
        if((year%4==0)&&(year%100!=0)){
            System.out.println(year+"是一个普通闰年");
        } else if (year%400==0) {
            System.out.println(year+"是一个世纪闰年");
        }else{
            System.out.println(year+"不是闰年");
        }
        int a = 1;
        while(a <= 10){
            System.out.println(a);
            a++;//条件要发生变化，不然会死循环
        }

        int b=1;
        int ret=1;
        int sum=0;
        while(b<=5){
            ret=ret*b;
            b++;
            sum=sum+ret;
        }
        System.out.println("ret="+ret);
        System.out.println("sum="+sum);

        int j=0;
        Scanner num3=new Scanner(System.in);
        int number=num3.nextInt();
        for(j=2;j<number;j++)
        {
            if(number%j==0){
                System.out.println("该数不是素数");
                break;
            }else{
                System.out.println("该数是素数");
            }
        }

        int k=0;
        int k1=0;
        for(k=2;k<=100;k++) {
            for(k1=2;k1<=k/2;k1++){
                if(k%k1==0){
                    break;
                }
            }
            if(k1>=k/2) {
                System.out.println(k);
            }
        }

        int year3=0;
        for(year3=1000;year3<=2000;year3++){
            if(year3/400==0||(year3%4==0&&year3/100!=0)) {
                System.out.println(year3);
            }
        }

        int i2=0;
        int sum1=0;
        for(i2=1;i2<=100;i2++){
            if(i2==99){
                sum1+=1;
            }else if(i2%10==9||i2/10==9) {
                sum1++;
            }
        }
        System.out.println("数字9出现了"+sum1+"次");