Java之---流程控制语句练习题01

  

   

    

     

    
    

     

      import java.util.Scanner;
     
    
   

    

     

    
    

     

      class demo3_1{
     
    
   

    

     

    
    

     
    
      public static void main(String[] argus){
     
    
   

    

     

    
    

     

              Scanner scanner=
      new Scanner(System.in);
     
    
   

    

     

    
    

     

              System.out.print(
      "请输入a b c:");
     
    
   

    

     

    
    

     
        
      double a=scanner.nextDouble();
     
    
   

    

     

    
    

     
        
      double b=scanner.nextDouble();
     
    
   

    

     

    
    

     
        
      double c=scanner.nextDouble();
     
    
   

    

     

    
    

     
        
      double delt=b*b-
      4*a*c;
     
    
   

    

     

    
    

     
        
      if(delt>
      0){
     
    
   

    

     

    
    

     
           
      double  r1=(-b + Math.sqrt(delt))/(
      2*a);
     
    
   

    

     

    
    

     
           
      double  r2=(-b - Math.sqrt(delt))/(
      2*a);
     
    
   

    

     

    
    

     

                 System.out.printf(
      "r1=%.2f,r2=%.2f",r1,r2);
     
    
   

    

     

    
    

     

                 }
      else 
      if(delt==
      0){
     
    
   

    

     

    
    

     
               
      double  r=(-b + Math.sqrt(delt))/(
      2*a);
     
    
   

    

     

    
    

     

                      System.out.printf(
      "r=%.2f",r);
     
    
   

    

     

    
    

     

                      }
      else{
     
    
   

    

     

    
    

     

                          System.out.printf(
      "没有实数解！");
     
    
   

    

     

    
    

     

                      }
     
    
   

    

     

    
    

     

              }
     
    
   

    

     

    
    

     
 
     
    
   

    

     

    
    

     

          }
     
    
  

  

   

    

     

    
    

     

      import java.util.Scanner;
     
    
   

    

     

    
    

     

      class demo3_2{
     
    
   

    

     

    
    

     
    
      public static void main(String[] args){
     
    
   

    

     

    
    

     

              Scanner scanner=
      new Scanner(System.in);
     
    
   

    

     

    
    

     

              System.out.println(
      "Enter a,b,c,d,e,f:");
     
    
   

    

     

    
    

     
        
      double a=scanner.nextDouble();
     
    
   

    

     

    
    

     
        
      double b=scanner.nextDouble();
     
    
   

    

     

    
    

     
        
      double c=scanner.nextDouble();
     
    
   

    

     

    
    

     
        
      double d=scanner.nextDouble();
     
    
   

    

     

    
    

     
        
      double e=scanner.nextDouble();
     
    
   

    

     

    
    

     
        
      double f=scanner.nextDouble();
     
    
   

    

     

    
    

     
        
      double A=(a*d-b*c);
     
    
   

    

     

    
    

     
        
      double B=(e*d-b*f);
     
    
   

    

     

    
    

     
        
      double C=(a*f-e*c);
     
    
   

    

     

    
    

     
        
      double x;
     
    
   

    

     

    
    

     
        
      double y;
     
    
   

    

     

    
    

     
        
      if(A!=
      0){
     
    
   

    

     

    
    

     

                  x=B/A;
     
    
   

    

     

    
    

     

                  y=C/A;
     
    
   

    

     

    
    

     

                  System.out.println(
      "x is" + x +
      " and y is" + y);
     
    
   

    

     

    
    

     
 
     
    
   

    

     

    
    

     

              }
      else{
     
    
   

    

     

    
    

     

                  System.out.println(
      "方程式无解");
     
    
   

    

     

    
    

     

              }
     
    
   

    

     

    
    

     
 
     
    
   

    

     

    
    

     

          }
     
    
   

    

     

    
    

     

      }
     
    
  

分析：

数据：今天的周几  未来的天数 未来的周几

       （0+12）%7=5

       （今天的周几+未来的天数）%7=未来的周几

步骤：

1.输入今天是周几

2.输入未来的几天

3.打印未来的几天是周几

 

  

   

    

     

    
    

     
 
     
    
   

    

     

    
    

     
 
      import java.util.Scanner;
     
    
   

    

     

    
    

     

      class demo3_3{
     
    
   

    

     

    
    

     
    
      public static void main(String[] argus){
     
    
   

    

     

    
    

     
        
      //1.
     
    
   

    

     

    
    

     

              Scanner scanner=
      new Scanner(System.in);
     
    
   

    

     

    
    

     

              System.out.print(
      "今天是周几：");
     
    
   

    

     

    
    

     
        
      int today=scanner.nextInt();
     
    
   

    

     

    
    

     
        
      //2.
     
    
   

    

     

    
    

     

              System.out.print(
      "未来的几天：");
     
    
   

    

     

    
    

     
        
      int future=scanner.nextInt();
     
    
   

    

     

    
    

     
        
      //3.
     
    
   

    

     

    
    

     
        
      int futureDay=(today+future)%
      7;
     
    
   

    

     

    
    

     

              String todayStr=
      "";
     
    
   

    

     

    
    

     

              String futureDayStr=
      "";
     
    
   

    

     

    
    

     
        
      if(today==
      0){
     
    
   

    

     

    
    

     

                  todayStr=
      "周日";
     
    
   

    

     

    
    

     

              }
      else 
      if(today==
      1){
     
    
   

    

     

    
    

     

                  todayStr=
      "周一";
     
    
   

    

     

    
    

     

              }
      else 
      if(today==
      2){
     
    
   

    

     

    
    

     

                  todayStr=
      "周二";
     
    
   

    

     

    
    

     

              }
      else 
      if(today==
      3){
     
    
   

    

     

    
    

     

                  todayStr=
      "周三";
     
    
   

    

     

    
    

     

              }
      else 
      if(today==
      4){
     
    
   

    

     

    
    

     

                  todayStr=
      "周四";
     
    
   

    

     

    
    

     

              }
      else 
      if(today==
      5){
     
    
   

    

     

    
    

     

                  todayStr=
      "周五";
     
    
   

    

     

    
    

     

              }
      else 
      if(today==
      6){
     
    
   

    

     

    
    

     

                  todayStr=
      "周六";
     
    
   

    

     

    
    

     

              }
     
    
   

    

     

    
    

     
        
      if(futureDay==
      0){
     
    
   

    

     

    
    

     

                  futureDayStr=
      "周日";
     
    
   

    

     

    
    

     

              }
      else 
      if(futureDay==
      1){
     
    
   

    

     

    
    

     

                  futureDayStr=
      "周一";
     
    
   

    

     

    
    

     

              }
      else 
      if(futureDay==
      2){
     
    
   

    

     

    
    

     

                 futureDayStr=
      "周二";
     
    
   

    

     

    
    

     

              }
      else 
      if(futureDay==
      3){
     
    
   

    

     

    
    

     

                 futureDayStr=
      "周三";
     
    
   

    

     

    
    

     

              }
      else 
      if(futureDay==
      4){
     
    
   

    

     

    
    

     

                  futureDayStr=
      "周四";
     
    
   

    

     

    
    

     

              }
      else 
      if(futureDay==
      5){
     
    
   

    

     

    
    

     

                  futureDayStr=
      "周五";
     
    
   

    

     

    
    

     

              }
      else 
      if(futureDay==
      6){
     
    
   

    

     

    
    

     

                  futureDayStr=
      "周六";
     
    
   

    

     

    
    

     

              }
     
    
   

    

     

    
    

     

              System.out.printf(
      "今天是" + todayStr + 
      ",未来的日子是" + futureDayStr );
     
    
   

    

     

    
    

     
         
     
    
   

    

     

    
    

     

          }
     
    
   

    

     

    
    

     

      }
     
    
  

分析：

12345

12345%10=5 12345/10=1234

1234%10=4  1234/10=123

123%10=3   123/10=12

12%10=2    12/10=1

1%10=1     1/10=0

54321

5*10000+4*1000+3*100+2*10+1

(5*1000+4*100+3*10+2)*10+1

((5*100+4*10+3)*10+2)*10+1

(((5*10+4)*10+3)*10+2)*10+1

((((0*10+5)*10+4)*10+3)*10+2)*10+1

 

sum=0

sum=sum*10+5;   //5

sum=sum*10+4;   //54

sum=sum*10+3;   //543

sum=sum*10+2;   //5432

sum=sum*10+1;   //54321

  

   

    

     

    
    

     
 
     
    
   

    

     

    
    

     

      import java.util.Scanner;
     
    
   

    

     

    
    

     

      class demo3_4{
     
    
   

    

     

    
    

     
    
      public static void main(String[] args){
     
    
   

    

     

    
    

     
        
      //1.输入一个数字
     
    
   

    

     

    
    

     

              Scanner scanner=
      new Scanner(System.in);
     
    
   

    

     

    
    

     

              System.out.print(
      "请输入一个数字：");
     
    
   

    

     

    
    

     
        
      int num=scanner.nextInt();
     
    
   

    

     

    
    

     
        
      int temp=num;  
      //给num备份
     
    
   

    

     

    
    

     
        
      //2.拼接出该数字的反序
     
    
   

    

     

    
    

     
        
      int sum=
      0;
     
    
   

    

     

    
    

     

              sum=sum*
      10+num%
      10;
     
    
   

    

     

    
    

     

              num/=
      10;
     
    
   

    

     

    
    

     

              sum=sum*
      10+num%
      10;
     
    
   

    

     

    
    

     

              num/=
      10;
     
    
   

    

     

    
    

     

              sum=sum*
      10+num%
      10;
     
    
   

    

     

    
    

     

              num/=
      10;
     
    
   

    

     

    
    

     
       
      /* sum=sum*10+num%10;
     
    
   

    

     

    
    

     

       num/=10;
     
    
   

    

     

    
    

     

       sum=sum*10+num%10;
     
    
   

    

     

    
    

     

       num/=10;
     
    
   

    

     

    
    

     

       sum=sum*10+num%10;
     
    
   

    

     

    
    

     

       num/=10;*/
     
    
   

    

     

    
    

     
        
      if(sum==temp){
     
    
   

    

     

    
    

     

                  System.out.println(
      "是回文");
     
    
   

    

     

    
    

     

              }
      else{
     
    
   

    

     

    
    

     

                  System.out.println(
      "不是回文");
     
    
   

    

     

    
    

     

              }
     
    
   

    

     

    
    

     

          }
     
    
   

    

     

    
    

     

      }
     
    
  

分析：

数据：电脑随机产生的一个数字com 用户输入的一个数字usr

    0 1 2

    剪刀 石头 布

步骤：

1.提示用户输入一个数字

2.计算机随机产生一个数字

3.将两个数字进行对比，分输赢

    平局  com==usr

    用户赢 usr=0 com=2 | usr=1 com=0 | usr=2 com=1

    用户输 剩下的都是用户输

 

随机数

    Math.random() [0,1.0)*3 -> [0,3.0)->(int)[0,3.0)

    Random nextInt(n)

    本题使用： int num=(int)(Math.random()*3);

    System.out.println(num);

 

   

    

     

      

     
     

      
 
      
     
    

     

      

     
     

      

       import java.util.*;
      
     
    

     

      

     
     

      

       class demo3_6{
      
     
    

     

      

     
     

      
    
       public static void main(String[] args){
      
     
    

     

      

     
     

      
        
       //1.
      
     
    

     

      

     
     

      

               Scanner scanner=
       new Scanner(System.in);
      
     
    

     

      

     
     

      

               System.out.print(
       "请输入 剪刀0 石头1 布2：");
      
     
    

     

      

     
     

      
        
       int usr=scanner.nextInt();
      
     
    

     

      

     
     

      
        
       //2.
      
     
    

     

      

     
     

      

               Random random=
       new Random();
      
     
    

     

      

     
     

      
        
       int com=random.nextInt(
       3);
      
     
    

     

      

     
     

      
 
      
     
    

     

      

     
     

      

               String usrStr=
       "";
      
     
    

     

      

     
     

      

               String comStr=
       "";
      
     
    

     

      

     
     

      
        
       switch(usr){
      
     
    

     

      

     
     

      
            
       case 
       0: 
       //if usr==0
      
     
    

     

      

     
     

      

                       usrStr=
       "剪刀"; 
      
     
    

     

      

     
     

      
                
       break;
      
     
    

     

      

     
     

      
            
       case 
       1:
       // if usr==1
      
     
    

     

      

     
     

      

                       usrStr=
       "石头";
      
     
    

     

      

     
     

      
                
       break;
      
     
    

     

      

     
     

      
            
       case 
       2:
       // if usr==2
      
     
    

     

      

     
     

      

                       usrStr=
       "布";
      
     
    

     

      

     
     

      
                
       break;
      
     
    

     

      

     
     

      

               }
      
     
    

     

      

     
     

      
        
       switch(com){
      
     
    

     

      

     
     

      
            
       case 
       0: 
      
     
    

     

      

     
     

      

                       comStr=
       "剪刀"; 
      
     
    

     

      

     
     

      
                
       break;
      
     
    

     

      

     
     

      
            
       case 
       1:
      
     
    

     

      

     
     

      

                       comStr=
       "石头";
      
     
    

     

      

     
     

      
                
       break;
      
     
    

     

      

     
     

      
            
       case 
       2:
      
     
    

     

      

     
     

      

                       comStr=
       "布";
      
     
    

     

      

     
     

      
                
       break;
      
     
    

     

      

     
     

      

               }
      
     
    

     

      

     
     

      
        
       //3.
      
     
    

     

      

     
     

      
        
       if(usr==com){
      
     
    

     

      

     
     

      

                   System.out.printf(
       "用户是%s，电脑是%s，平局",usrStr,comStr);
      
     
    

     

      

     
     

      

               }
       else 
       if(usr==
       0&&com==
       2 || usr==
       1&&com==
       0 || usr==
       2&&com==
       1){
      
     
    

     

      

     
     

      

                   System.out.printf(
       "用户是%s，电脑是%s，用户赢",usrStr,comStr);
      
     
    

     

      

     
     

      

               }
       else{
      
     
    

     

      

     
     

      

                   System.out.printf(
       "用户是%s，电脑是%s，用户输",usrStr,comStr);
      
     
    

     

      

     
     

      

               }
      
     
    

     

      

     
     

      

           }
      
     
    

     

      

     
     

      

       }
      
     
   

 

              

数据：圆的圆心 圆的半径 点的坐标 距离

步骤：

1.提示用户输入点的坐标

2.计算点到圆心之间的距离

3.判断距离和半径之间的关系

    距离>半径   点在圆外

    距离==半径  点在圆上

    距离<半径   点在圆内

   

    

     

      

     
     

      

       import java.util.Scanner;
      
     
    

     

      

     
     

      

       class demo3_8{
      
     
    

     

      

     
     

      
    
       public static void main(String[] args){
      
     
    

     

      

     
     

      
        
       //1.
      
     
    

     

      

     
     

      

               Scanner scanner=
       new Scanner(System.in);
      
     
    

     

      

     
     

      

               System.out.print(
       "请输入坐标点：");
      
     
    

     

      

     
     

      
        
       double x=scanner.nextDouble();
      
     
    

     

      

     
     

      
        
       double y=scanner.nextDouble();
      
     
    

     

      

     
     

      
        
       //2.
      
     
    

     

      

     
     

      
        
       double xo=
       0;
      
     
    

     

      

     
     

      
        
       double yo=
       0;
      
     
    

     

      

     
     

      
        
       double radius=
       10;
      
     
    

     

      

     
     

      
        
       double distance=Math.sqrt(Math.pow(x-xo,
       2)+Math.pow(y-yo,
       2));
      
     
    

     

      

     
     

      
        
       //3.
      
     
    

     

      

     
     

      
        
       if(distance>radius){
      
     
    

     

      

     
     

      

                   System.out.println(
       "点在圆外");
      
     
    

     

      

     
     

      

               }
       else 
       if(distance==radius){
      
     
    

     

      

     
     

      

                   System.out.println(
       "点在圆上");
      
     
    

     

      

     
     

      

               }
       else{
      
     
    

     

      

     
     

      

                   System.out.println(
       "点在圆内");
      
     
    

     

      

     
     

      

               }
      
     
    

     

      

     
     

      

           }
      
     
    

     

      

     
     

      

       }