Java基础入门篇之逻辑控制练习题与猜数字游戏

int year = 2000;
if (year % 100 == 0) {
    // 判定世纪闰年
    if (year % 400 == 0) {
        System.out.println("是闰年");
   } else {
        System.out.println("不是闰年");
   }
} else {
    // 普通闰年
    if (year % 4 == 0) {
        System.out.println("是闰年");
   } else {
        System.out.println("不是闰年");
   }
}

int n = 1;
int ret = 1;
while(n <= 5){
  ret = ret * n;
  n++;
  }
  System.out.println(ret);

  int k =1;
  int sum = 0;
  // 外层循环负责求阶乘的和
  while(k <= 5) {
     int n = 1;
     int ret = 1;
     // 里层循环负责完成求阶乘的细节. 
     while (n <= k) {
        ret = ret * n;
        n++;
     }
     k++;
     sum = sum + ret;
  }
  System.out.println(sum);

int result = 1;
for (int i = 1; i <= 5; i++) {
    result *= i;
}
System.out.println("result = " + result);

int sum = 0;

for (int i = 1; i <= 5; i++) {
    int tmp = 1;
    for (int j = 1; j <= i; j++) {
        tmp *= j;
   }
    sum += tmp;
}

System.out.println("sum = " + sum);

public class TestDemo {
    public static void main(String[] args) {
        int n = 19;
        int i = 2;
        for (; i <=Math.sqrt(n) ; i++) {
            if (n % i == 0){
                break;
            }
        }
        //有两种情况  1、 不符合循环条件 2、因为遇到了 break
        if (i > Math.sqrt(n)){
            System.out.println(n + " 是素数！ ");
        }
    }
}

        for (int n = 1; n <= 100; n++) {
            //int n = 9;
            int i = 2;
            for (; i <= Math.sqrt(n); i++) {
                if(n % i == 0) {
                    break;
                }
            }
            //有几种情况 ？ 2--》  1、 不符合循环条件 2、因为遇到了 break
            if(i > Math.sqrt(n)) {
                System.out.println(n + " 是素数！ ");
            }
        }

         for (int i = 1; i <= 999999; i++) {
            //i == 123
            int count = 0;//记录位数
            int tmp = i;
            while (tmp != 0) {
                tmp /= 10;
                count++;
            }
            tmp = i;//123
            int sum = 0;
            while (tmp != 0) {
                sum += Math.pow(tmp % 10, count);
                tmp /= 10;
            }
            if (sum == i) {
                System.out.println(i);
            }
        }

int n = -1;
int count = 0;
while (n != 0) {
     n = n & (n-1);
     count++;
}
System.out.println(count);

 public class TestDemo {
      public static void main(String[] args) {
            Random random = new Random();
            Scanner scanner = new Scanner(System.in);
            int randNum = random.nextInt(101);//[0,101)
             //50-100的随机数   random.nextInt(50)--[0,50)  + 50;
            while(true){
                   System.out.println("请输入你要猜的数字");
                   int sum = scanner.nextInt();
                   if(sum < randNum){
                       System.out.println("猜小了");
                   }else if(sum == randNum){
                       System.out.println("猜对了");
                       break;
                    }else{
                        System.out.println("猜大了");
                     }
           }
      }
}