第四次作业

1.使用for循环计算1-100的和，除了以3结尾的那些数

package abc;

public class work1 {

    public static void main(String[] args) {
        // TODO Auto-generated method stub
        int sum=0;
       for (int i = 1; i <101; i++) {
         if(i%10!=3)
             sum+=i;
    }
       System.out.println("和是"+sum );
    } 

}

2.2.使用二重循环输出以下图形

   *
  ***
 *****
*******


*****
****
***
**
*

package abc;

public class work2 {

    public static void main(String[] args) {
        // TODO Auto-generated method stub
        for (int i = 1; i <=4; i++) {
            for (int j = 1; j <=4-i ; j++) {
                System.out.print(" ");
            }
                for (int k = 1; k <=2*i-1; k++) {
                    System.out.print("*");
                
            }
            System.out.println();
        }
    
        for (int i = 1; i <=5; i++) {
            for (int j = 1; j <=6-i; j++) {
                System.out.print("*");
            }
            System.out.println();
        }
        
    } 

}

3.循环输入学生姓名，直到输入‘Q’程序结束。

package abc;

import java.util.Scanner;

public class work3 {

    public static void main(String[] args) {
        // TODO Auto-generated method stub
          Scanner input=new Scanner(System.in);
        for (;; ) 
        {
        System.out.println("请输入学生姓名");
          char name=input.next().charAt(0);
          if(name=='Q')
              break;
        }
        System.out.println("程序结束");
    }

}

4.输入5个学生成绩，求和，当输入不合法的时候，提示输入错误重新输入。

package abc;

import java.util.Scanner;

public class work4 {

    public static void main(String[] args) {
        // TODO Auto-generated method stub
            Scanner input=new Scanner(System.in);
            System.out.println("请输入学生成绩");
            int sum=0;
            for (int i =1; i <=5; i++) {
             int gra=input.nextInt();
            
            while (gra>100||gra<0) {
                System.out.println("输入不合法请重新输入");
                gra=input.nextInt();
            
            }
            sum+=gra;
            }    
            System.out.println("sum="+sum);
    }
    

}

5.计算 1+1/（1+2） +  1/（1+2+3）  +1/（1+2+3+4）+…………+1/（1+2+....+10）

package abc;

public class work5 {

    public static void main(String[] args) {
        // TODO Auto-generated method stub
       double sum=0;
       double sum1=0;
       for (int i =1; i <=10; i++) {
        sum+=i;                         
        sum1=1/sum+sum1;   
    }
       System.out.println("sum1="+sum1);
    }

}

6.产生一个1-99的随机数，猜数字，若大了就提示“大了点”，若小了就提示“小了点”直到猜对为止。（判断猜的次数，如果1-3次，提示太棒了 如果5-8次 一般般 如果8次以上 太笨了）

package abc;

import java.util.Random;
import java.util.Scanner;

public class work6 {

    public static void main(String[] args) {
        // TODO Auto-generated method stub
        Random r = new Random();
        int x = r.nextInt(99)+1;
        Scanner input = new Scanner(System.in);
        int n = input.nextInt();
        int ci=1;
        while (n != x) {
        if (n > x) {
        System.out.println("大一点");
        } else if (n < x) {
        System.out.println("小一点");
        }
        n = input.nextInt();
        if (n == x) {
        System.out.println("猜对了");
        }
        ci++;
        }
        if(ci>0&&ci<=3){
        System.out.println("太棒了");
        }else if(ci>=4&&ci<=8){
        System.out.println("一般般");
        }if(ci>8){
        System.out.println("太笨了");
        }
        System.out.println("猜的次数为"+ci);
        System.out.println("要猜的数是"+x);
        }
        
    
    
    
    

}

7.输入一个数，判断是不是质数（只能被1和自身整除的数是质数)

package abc;

import java.util.Scanner;

public class work7 {

    public static void main(String[] args) {
        // TODO Auto-generated method stub
         Scanner input = new Scanner(System.in);
            System.out.println("输入一个数");
            int num = input.nextInt();
            boolean isPrime = true;
            if (num == 1) {
                isPrime = false;
            }
            for (int i = 2; i <= num - 1; i++) {
                if (num % i == 0) {
                    isPrime = false;
                    break;
                }
            }

            if (isPrime) {
                System.out.println(num + "是质数");
            } else {
                System.out.println(num + "不是质数");
            }
            
    }

}

8.求斐波那契数列第二十项是什么？斐波那契数列： 1  1  2  3  5 ....

package abc;

public class work8 {

    public static void main(String[] args) {
        // TODO Auto-generated method stub
              int a=1;
              int b=1;
              int c=0;
             
              for (int i =1; i <=18; i++) {  
                c=a+b;
                a=b;
                b=c;
                
            }
              System.out.println("第十八项为"+c);
    }
    

}