java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 wxl;

 

public class ctt {

 

    public static void main(String[] args) {

        // TODO Auto-generated method stub

        int sum=0;

        for (int i = 1; i <=100; i++) {

            if (i%10==3)

                continue;

                sum = sum+i;

               

           

           

           

        }

        System.out.println(sum);

 

    }

 

}

 

 

 

2.使用二重循环输出以下图形

 

   *

  ***

 *****

*******

 

public class ctt {

 

    public static void main(String[] args) {

        // TODO Auto-generated method stub

        for (int i = 1; i <=4; i++) {

            for (int j = 0; j <=4-i; j++) {

                System.out.print(" ");

            }

            for (int k = 1; k <=2*i-1; k++) {

                System.out.print("*");

               

            }

            System.out.println();

        }

    }

   

}

 

 

 

 

 

*****

****

***

**

*

public class ctt {

 

    public static void main(String[] args) {

        // TODO Auto-generated method stub

        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。

import java.util.Scanner;

 

public class ctt {

 

    public static void main(String[] args) {

        // TODO Auto-generated method stub

        Scanner input=new Scanner(System.in);

        System.out.println("请连续输入学生姓名");

        while (true) {

            String name=input.next();

            if(name.equals("Q"))

            {

                System.out.println("程序结束");

            }

           

        }

    }

 

}

 

 

 

4.输入5个学生成绩，求和，当输入不合法<0   >100的时候，提示输入错误重新输入。

import java.util.Scanner;

 

public class ctt {

 

    public static void main(String[] args) {

        // TODO Auto-generated method stub

        Scanner input=new Scanner(System.in);

        System.out.println("请输入五个学生的成绩");

        int sum=0;

        int i=0;

        while (i<=4) {

            System.out.println("请输入第"+(i+1)+"个学生的成绩");

            int a=input.nextInt();

            if (a<0||a>100) {

                System.out.println("输入错误，请重新输入");

               

            }

            else {

                i++;

                sum+=a;

            }

           

        }

        System.out.println("学生的总成绩为："+sum);

    }

 

}

 

 

 

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

public class ctt {

 

    public static void main(String[] args) {

        // TODO Auto-generated method stub

        double sum=0;

        double a=0;

        for (int i = 1; i <=10; i++) {

            sum+=i;

            a+=1/sum;

        }

        System.out.println(a);

    }

 

}

 

 

 

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）

import java.util.Random;

import java.util.Scanner;

 

public class ctt {

 

    public static void main(String[] args) {

        // TODO Auto-generated method stub

        Random r=new Random();

        Scanner input=new Scanner(System.in);

        int rand=r.nextInt(100);

        int num=0;

        while (true) {

            int i=input.nextInt();

            if (i==rand) {

                System.out.println("猜对了");

                return;

               

            }

            else if(i<rand) {

                System.out.println("猜小了");

            }

            else {

                System.out.println("猜大了");

                break;

            }

           

        }

        System.out.println("一共循环了"+num+"次");

        if (num<=3) {

            System.out.println("太棒了");

           

        } else if(num>3&&num<6) {

            System.out.println("还可以");

 

        }else {

            System.out.println("太笨了");

        }

    }

 

}

 

 

 

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）   12

import java.util.Random;

import java.util.Scanner;

 

public class ctt {

 

    public static void main(String[] args) {

        // TODO Auto-generated method stub

        Scanner input=new Scanner(System.in);

        System.out.println("请输入一个数");

        int num=input.nextInt();

        boolean zhishu=true;

        if (num==1) {

            zhishu=false;

        }

        for (int i = 2; i <=num-1; i++) {

            if (num%i == 0) {

                zhishu=false;

                break;

               

            }

           

        }

        if (zhishu) {

            System.out.println(num+"是质数");

           

        }else {

            System.out.println(num+"不是质数");

        }

       

    }

 

}

 

 

 

8.求裴波那契数列的第20项是什么。裴波那契数列，1,1,2,3,5,8,13，21……

public class ctt {

 

    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(c);

    }

 

}