Day12 control flow if switch while do While guessing numbers game

Control process

Sequential structure

All programs are executed in sequence

if Statement selection structure

Single choice statement

if(a>0){System.out.println(“hello”);}

package com.ckw.blog.select;

import java.util.Scanner;

public class demo01 {
    public static void main(String[] args) {
        int score = 0;
        Scanner scanner = new Scanner(System.in);
        System.out.println(" Please enter a number ");
        score = scanner.nextInt();

        if (score>40){
            System.out.println(" This is larger than 40");
        }

        scanner.close();
    }
}

Double choice statement

if(a>0){System.out.println(“hello”);}

else{System.out.println(“no”);};

package com.ckw.blog.select;

import java.util.Scanner;

public class demo01 {
    
    public static void main(String[] args) {
    
        int score = 0;
        Scanner scanner = new Scanner(System.in);
        System.out.println(" Please enter a number ");
        score = scanner.nextInt();

        if (score>40){
    
            System.out.println(" This is larger than 40");
        }else {
    
            System.out.println(" This is less than 40");
        }

        scanner.close();
    }
}

Multi conditional statement

if(a>0){System.out.println(“hello”);}

else if(a>1){System.out.println(“no1”);}

else if(a>2){System.out.println(“no2”);}

else{System.out.println(“no3”);};

package com.ckw.blog.select;

import java.util.Scanner;

public class demo01_text {
    
    public static void main(String[] args) {
    
        int score = 0;// Initialize grades 
        Scanner scanner =new Scanner(System.in); // introduce Scanner class 
        while (scanner.hasNextInt()){
      // If the input is an integer, it will run all the time , Otherwise jump out of the loop 
        score = scanner.nextInt();  // Open input and assign 
        if (score>=90){
    
            System.out.println("A level ");
        }else if(score<90 && score>=80){
    
            System.out.println("B level ");
        }else if (score<80 && score>=70){
    
            System.out.println("C level ");
        }else if(score<70 && score>=60){
    
            System.out.println("D level ");
        }else if (score<60 && score>=0){
    
            System.out.println(" The result is not up to standard ");
        }else {
    
            System.out.println(" The score entered is not legal ");
        }}
        scanner.close();// Turn off input 
    }
}

Switch sentence

Determine whether a variable is equal to a value in a series of values , Each value becomes a branch .

switch Supported variable types in statement ：

1. byte int short perhaps char
2. from JAVA 7 Start switch Support string String Type .
3. case The label must be a string or literal

switch(expression expression ){

case value Constant :{};break; // Optional

case value Constant :{};break;// Optional

default:{}// Optional

package com.ckw.blog.select;
import java.util.Scanner;

public class demo02 {
    
    public static void main(String[] args) {
    
        String str = "K";
        Scanner scanner = new Scanner(System.in);
        str = scanner.next();
        switch (str){
    
            case "A":// Matching character 
                System.out.println(" Good grades ");
                break;// If not, it will appear case through 
            case "B":
                System.out.println(" Average grade ");
                break;
            case "D":
                System.out.println(" Average results ");
                break;
            case "E":
                System.out.println(" Achievement deviation ");
                break;
            case "F":
                System.out.println(" Failing in grades ");
                break;
            default:
                System.out.println(" Unknown input ");
        }
    }
}

switch Be careful

1. case The result is characters , There is no need for brackets
2. case The result requires : Number .
3. default Although it is optional , But still add as code integrity

Switch Follow if The difference between ：

• if Used to compare numbers , As an option

• switch It is mainly used to match multiple character results , Make a choice

  （ The source code is still used if As a compiler ）

switch Follow if Cooperate to output the score code

package com.ckw.blog.select;

import java.util.Scanner;

public class study01 {
    
    public static void main(String[] args) {
    
        int score = 0;// Initialize grades 
        String str = "k";// Initialization level 
        Scanner scanner =new Scanner(System.in); // introduce Scanner class 
          while (scanner.hasNextInt()){
    // If the input is an integer, it will run all the time , Otherwise jump out of the loop 
            score = scanner.nextInt();  // Open input and assign 
            if (score>=90&&score<=100){
    
               str = "A";
            }else if(score<90 && score>=80){
    
                str = "B";
            }else if (score<80 && score>=70){
    
                str = "C";
            }else if(score<70 && score>=60){
    
                str = "D";
            }else if (score<60 && score>=0){
    
                str = "E";
            }else {
    
                str = "F";;
            }
            switch (str){
    
            case "A":// Matching character 
                System.out.println(" Good grades ");
                break;// If not, it will appear case through 
            case "B":
                System.out.println(" Average grade ");
                break;
            case "C":
                System.out.println(" Average results ");
                break;
            case "D":
                System.out.println(" Achievement deviation ");
                break;
            case "E":
                System.out.println(" Failing in grades ");
                break;
            default:
                System.out.println(" Unknown input ");
        }}
        scanner.close();// Turn off input 
    }
    }

The game of guessing numbers

The first one is if structure .

1. while
2. if（）{}else if（）{}
3. Relationship identifier

package com.ckw.blog.select;

import java.util.Scanner;

public class demo01 {
    
    public static void main(String[] args) {
    
        int score = 0;
        int nub = 40;
        Scanner scanner = new Scanner(System.in);
        System.out.println(" Please enter a number ");
        while (score!=nub){
    
            score = scanner.nextInt();
            if(score>nub){
    
                System.out.println(" big ");
            }else if(score<nub){
    
                System.out.println(" The small ");
            }
        }
        System.out.println(" Congratulations, you're right ");


        scanner.close();
    }
}

Loop structure

while Loop statement

while（ Boolean expression ）{ result }

package com.ckw.blog.select;

public class while001 {
    
    public static void main(String[] args) {
    
        int a  = 0;
	while(a<100){
    System.out.println(a)};
    }
}

do…while…

do{ Calculation formula }while( Boolean expression )

Execute once before entering the loop

package com.ckw.blog.select;

public class while001 {
    
    public static void main(String[] args) {
    
        int a  = 0;

        do{
    a++;System.out.println(a);}while(a>=1&&a<100);
// Execute the code once first , If the condition is turn, Then enter the cycle 
    }
}

do…while Follow while The difference between

while It's judgment before execution ,do…while It's execution before judgment

do…while The run will execute a cycle at least once

package com.ckw.blog.select;

public class while001 {
    
    public static void main(String[] args) {
    
        int a  = 0;
        while (a>0&&a<100){
    
            System.out.println(" I'm the result 1 Of ");
            System.out.println(a);
            a++;
        }
        do{
    a++;
            System.out.println(" I'm the result 2 Of ");
            System.out.println(a);}while (a>0&&a<100);
// Execute the code once first , If the condition is turn, Then enter the cycle 
    }
}