Language foundation day 5:

Review:

1. Scanner receives user data: 3 steps in total

2. Branch structure:

   • If... else if structure: multiple paths
   • switch... case structure: multiple paths
     Advantages: high efficiency and clear structure
     Disadvantages: you can only judge the equality of integers
     break: jump out of switch

3. Loop: repeatedly execute a piece of the same or similar code multiple times

4. Three elements of circulation:

   • Initialization of loop variables
   • Conditions of the loop (based on loop variables)
   • Change of cycle variable (towards the end of the cycle)

     Loop variable: the number that changes repeatedly throughout the loop

5. Cycle structure:

   • while structure: judge first and then execute. It may not be executed at all
   • do... while structure: execute first and then judge, at least once

     When element 1 is the same as element 3, do... while is preferred

Notes:

1. Cycle structure:

   • for structure: high application rate and number related cycle
     • Syntax:
       ​ // 1 2 3
       Element (1; for; 3){
       Statement block / loop body ------------- code executed repeatedly 4
       ​ }
     • Execution process:
       ​ 1243243243243243243...2
     • Code demonstration:

       //The loop variable i in the for loop has the scope only in the current for loop
       for(int i=1;i<=9;i++){
           System.out.println(i+"*9="+i*9);
       }
       for(int i=1;i<=9;i+=2){
           System.out.println(i+"*9="+i*9);
       }
       for(int i=9;i>=1;i--){
           System.out.println(i+"*9="+i*9);
       }
       
       for(int times=0;times<5;times++){
           System.out.println("Action is the ladder of success");
       }
       System.out.println("Continue execution...");
       /*
       Execution process:
       times=0  true  output
           times=1  true  output
           times=2  true  output
           times=3  true  output
           times=4  true  output
           times=5  false for End of cycle
           Output continue
       */
       
       //Special format of for: --------- understand
       int i=1;
       for(;i<=9;i++){
           System.out.println(i+"*9="+i*9);
       }
       for(int i=1;i<=9;){
           System.out.println(i+"*9="+i*9);
           i++;
       }
       for(;;){ //An unconditional cycle is an endless cycle
           System.out.println("I want to study...");
       }
       
       for(int i=1,j=5;i<=5;i+=2,j-=2){
       }
       /*
         i=1,j=5  true
         i=3,j=3  true
         i=5,j=1  true
         i=7,j=-1 false
        */
       

2. Selection rules of three cycle structures:

   • First, check whether the cycle is related to the number of times:
     • If relevant ------------------------------- go directly to for
     • If not, see whether element 1 and element 3 are the same:
       • If the same ----------------------- go directly to do... while
       • If different ----------------------- go directly to while

3. break: jump out of loop

   for(int i=1;i<=9;i++){
       if(i==4){ //Under certain conditions, end the cycle ahead of time
           break;
       }
       System.out.println(i+"*9="+i*9);
   }
   /* 
     i=1  true  1*9=9
     i=2  true  2*9=18
     i=3  true  3*9=27
     i=4  true
   */        
   

   continue: skip the remaining statements in the loop body and enter the next loop

   //Output the multiplication table of 9, as long as it cannot be divided by 3
   for(int i=1;i<=9;i++){
       if(i%3!=0){
           System.out.println(i+"*9="+i*9);
       }
   }
   //Output the multiplication table of 9 and skip the multiplication table that can be divided by 3
   for(int i=1;i<=9;i++){
       if(i%3==0){
           continue; //Skip the remaining statements in the loop body and enter the next loop
       }
       System.out.println(i+"*9="+i*9);
   }
   /*
       i=1  1*9=9
       i=2  2*9=18
       i=3
       i=4  4*9=36
       i=5  5*9=45
       i=6
       i=7  7*9=63
       i=8  8*9=72
       i=9
       i=10
   */
   

4. Random adder case:

   package day05;
   import java.util.Scanner;
   //Random adder
   public class Addition {
       public static void main(String[] args) {
           Scanner scan = new Scanner(System.in);
           int score = 0; //Total score
           for(int i=1;i<=10;i++) { //10 times
               int a = (int)(Math.random()*100); //Addend a, between 0 and 99
               int b = (int)(Math.random()*100); //Addend b
               int result = a+b; //Save the correct answer
               System.out.println("("+i+")"+a+"+"+b+"=?"); //1) Set a topic
   
               System.out.println("Count it!----input-1 Can end in advance");
               int answer = scan.nextInt(); //2) Answer questions
   
               if(answer==-1){ //3) Judgment question
                   break;
               }
               if(answer==result){
                   System.out.println("bingo");
                   score += 10; //If you answer one question correctly, 10 points will be added
               }else{
                   System.out.println("Wrong answer");
               }
           }
           System.out.println("The total score is:"+score);
       }
   }
   

5. Nested loop:

6. Array:

Essence notes:

1. Cycle structure:
   • for structure: high application rate and number related cycle
2. Selection rules of three cycle structures:
   • First, check whether the cycle is related to the number of times:
     • If relevant ------------------------------- go directly to for
     • If not, see whether element 1 and element 3 are the same:
       • If the same ----------------------- go directly to do... while
       • If different ----------------------- go directly to while
3. break: jump out of loop
   continue: skip the remaining statements in the loop body and enter the next loop
4. Nested loop:
5. Array: