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package quiz1;
 
import java.util.Scanner;
 
//문자열 입력 받아서 대 <---> 소문자 출력하는 프로그램 
public class Ex01_API {
 
    public static void main(String[] args) {
 
        Scanner sc = new Scanner(System.in);
        
        char[] input = null;
        
        System.out.print("input String => ");
        String str = sc.next();
        input = str.toCharArray();
        
        for (int i=0; i<str.length(); i++) {
            
            if( (65 <= (int)input[i]) && ((int)input[i] <= 90)) {
                input[i] = str.toLowerCase().charAt(i);
                
            } else if ((97 <= (int)input[i]) && ((int)input[i] <= 122)){
                input[i] = str.toUpperCase().charAt(i);
 
            } else { 
                input[i] = str.charAt(i);
            }// if end
        } //for end 
 
        System.out.print("output String =>");
        
        for(int i=0; i<input.length; i++) {
        System.out.print(input[i]);
        }
    }
 
}
 
 cs

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Operation Program - java.io package의 BufferedReader + while(true) break; continue;  (0) 2021.01.27

<BMI.java>

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package quiz3.ex01.io;
 
 
//몸무게, 키 입력받아서 BMI 계산하기
public class Bmi2 {
 
    double weight = 0;
    double height = 0;
    double bmi = 0;
    String bmi_result = null;
    int num=0;
 
    // 생성자
    public Bmi2() {
 
    }
    
    public Bmi2(double weight, double height, int num) {
        this.num = num;
        this.weight = weight;
        this.height = height;
        bmiCalc(weight, height);
    }
    
 
    // getter, setter method
    public double getWeight() {
        return weight;
    }
 
    public void setWeight(double weight) {
        this.weight = weight;
    }
 
    public double getHeight() {
        return height;
    }
 
    public void setHeight(double height) {
        this.height = height;
    }
 
    public double getBmi() {
        return bmi;
    }
 
    public void setBmi(double bmi) {
        this.bmi = bmi;
    }
    
    public int getNum() {
        return num;
    }
 
    public void setNum(int num) {
        this.num = num;
    }
    
    
    //계산 처리
    public void bmiCalc(double w, double h) {
        bmi = w / ( (h/100.0) * (h/100.0) ) ;        
        bmiResult(bmi);
    }
    
    public void bmiResult(double bmi) {
        
        if(bmi < 18.5) {
            bmi_result = "체중부족";
        } else if(bmi >= 18.5 && bmi <= 22.9) {
            bmi_result = "정상";
        } else if(bmi >= 23.0 && bmi <= 24.9) {
            bmi_result = "과체중";
        } else {
            bmi_result = "비만";
        }
    }
    
    //출력 method
    public void display() {
        System.out.println("<<<<<" + num + "번째 정보>>>>>");
        System.out.println("▶몸무게: " + weight + "kg");
        System.out.println("▶키: " + height + "cm");
        System.out.printf("▶BMI: %.2f \n", bmi);
        System.out.println("▶판정: " + bmi_result);
    }
 
 
}
 
 cs

<Main.java>

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package quiz3.ex01.io;
 
import java.io.*;
import java.util.*;
 
public class Main2 {
 
    public static void main(String[] args) {
 
        Bmi2 b = new Bmi2();
 
        // ArrayList 생성
        ArrayList<Bmi2> list = new ArrayList<Bmi2>();
 
        int count = 0;
        int num = 0;
 
        // readLine()을 쓰기위해 BufferedReader 선언
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        
        // 파일 저장
        ObjectOutputStream bos = null;
        File f = new File("bmi결과.txt"); //저장할 파일(상대주소 - 현재 폴더에 저장됨)
 
        try {
            FileOutputStream fos = new FileOutputStream(f, true); // append mode -> 뒤에 차례로 계속 추가
            bos = new ObjectOutputStream(fos);
 
            System.out.println("-----------------BMI계산 프로그램-------------------");
            
            while (true)
                block: {
                    System.out.println("***원하는 메뉴를 입력해주세요***(1.추가, 2.삭제, 3.출력, 4.종료)");
                    num = Integer.parseInt(br.readLine());
 
                    switch (num) {
                    case 1: // 추가
                        count++;
 
                        System.out.print("키>> ");
                        double h = Double.parseDouble(br.readLine());
 
                        System.out.print("몸무게>> ");
                        double w = Double.parseDouble(br.readLine());
 
                        list.add(new Bmi2(w, h, count)); // list에 추가*****??->객체로 넣으면 그곳에있는 모든 값들이 list에 저장됨
 
                        bos.writeObject(b.weight); // 파일에 저장하기
                        bos.writeObject(b.weight);
                        bos.writeObject(b.bmi);
                        bos.writeObject(b.bmi_result);
                        System.out.println("bmi결과1.txt 저장 완료.");
                        break;
                        
                    case 2: // 삭제 - 삭제부분 입력값과 list안의 값 비교 코드 추가
                        if (list.isEmpty()) { // list안에 요소가 없다면
                            System.out.println("삭제할  정보가 없습니다.");
                            continue; // ->continue, break둘다 가능 
                        }
 
                        while (true) {
                            System.out.print("삭제하기를 원하는 정보의 번호를 입력하시오 ( 1 ~ ) : ");
                            int remove_num = Integer.parseInt(br.readLine()); // 삭제할 번호입력받음
 
                            for (int i = 0; i < list.size(); i++) { // list안의 모든 정보와 비교
 
                                if (remove_num == list.get(i).getNum()) {
                                    list.remove(i); //리스트에서 삭제 
                                    System.out.println("삭제되었습니다.");
                                    break block; //삭제한 후, 메뉴 선택 구문으로 돌아감 
                                }
                                continue; // i번째 번호와 같지 않으면, i+1번째번호와 다시 비교
                            } // for end
 
                            // list안의 모든 정보와 비교한후에도 같은 정보가 없다면
                            System.out.println("일치하는 정보가 없습니다.");
                        } // while end
                        
                    case 3: // 출력
                        if (list.isEmpty()) { // list안에 요소가 없다면
                            System.out.println("조회할 정보가 없습니다.");
                            continue; 
                        }
 
                        System.out.println("***전체 목록***");
                        for (int i = 0; i < list.size(); i++) {
                            list.get(i).display();
                            System.out.println();
                        }
                        break;
                        
                    case 4: // 종료
                        System.out.println("종료되었습니다.");
                        System.exit(0);
                        
                    default:
                        System.out.println("다시 입력해주세요.");
                    } // switch end
                } // while end
 
        } catch (
 
        Exception e) {
            e.printStackTrace();
        } finally {
            try {
                br.close();
                bos.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
 
    }
 
}
 
 cs

고민했던 코드 

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<Heart.java>

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package quiz1.thread;
 
public class Heart implements Runnable {
 
    @Override
    public void run() {
 
        try {
            while (true) {
                int i;
                System.out.println();
 
                for (i = 4; i < 10; i += 2) {
                    MakeHeart1(10 - i);
                    MakeHeart2(i * 2);
                    MakeHeart1((10 - i) * 2);
                    MakeHeart2(i * 2);
                    System.out.println();
                }
 
                for (i = 20; i >= 0; i -= 2) {
                    MakeHeart1(20 - i);
                    MakeHeart2(i * 2);
                    System.out.println();
                }
 
                Thread.sleep(500);
                
                for (i = 4; i < 10; i += 2) {
                    MakeHeart1(10 - i);
                    MakeHeart3(i * 2);
                    MakeHeart1((10 - i) * 2);
                    MakeHeart3(i * 2);
                    System.out.println();
                }
 
                for (i = 20; i >= 0; i -= 2) {
                    MakeHeart1(20 - i);
                    MakeHeart3(i * 2);
                    System.out.println();
                }
 
                Thread.sleep(500);
 
            }
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
 
    }
 
    public void MakeHeart1(int a) {
        int j;
        for (j = 0; j < a; j++) {
            System.out.print(" ");
        }
    }
 
    public void MakeHeart2(int a) {
        int j;
        for (j = 0; j <= a; j++) {
            System.out.print("♡");
        }
    }
 
    public void MakeHeart3(int a) {
        int j;
        for (j = 0; j <= a; j++) {
            System.out.print("♥");
        }
    }
 
}
 
 cs

<HeartMain.java>

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package quiz1.thread;
 
public class HeartMain {
 
    public static void main(String[] args) {
        
        new Thread(new Heart()).start();
 
    }
}
 
 cs

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<Score.java>

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package quiz2.ex01.score;
 
//수정하기를 구체적으로 나누기 
public class Score_2 {
 
    protected String name;
    protected int kor, eng, com, tot;
    protected double avg;
    protected char grade;
 
    // 생성자
    public Score_2() {
 
    }
 
    public Score_2(String name, int kor, int eng, int com, int tot, double avg, char grade) {
        super();
        this.name = name;
        this.kor = kor;
        this.eng = eng;
        this.com = com;
        this.tot = tot;
        this.avg = avg;
        this.grade = grade;
    }
    
    public Score_2(String name, int kor, int eng, int com) {
        this.name = name;
        this.kor = kor;
        this.eng = eng;
        this.com = com;
    }
 
    
    
    public String getName() {
        return name;
    }
 
    public void setName(String name) {
        this.name = name;
    }
 
    public int getKor() {
        return kor;
    }
 
    public void setKor(int kor) {
        this.kor = kor;
    }
 
    public int getEng() {
        return eng;
    }
 
    public void setEng(int eng) {
        this.eng = eng;
    }
 
    public int getCom() {
        return com;
    }
 
    public void setCom(int com) {
        this.com = com;
    }
 
    public int getTot() {
        return tot;
    }
 
    public void setTot(int tot) {
        this.tot = tot;
    }
 
    public double getAvg() {
        return avg;
    }
 
    public void setAvg(double avg) {
        this.avg = avg;
    }
 
    public char getGrade() {
        return grade;
    }
 
    public void setGrade(char grade) {
        this.grade = grade;
    }
 
    // output method
    public void display(int num) {
 
        System.out.println("\n\n****** " + (num + 1) + "번학생 " + name + " 님의 성적표 ******");
        System.out.println("Kor : " + kor + "\tEng : " + eng + "\tCom : " + com);
        System.out.print("Total : " + tot);
        System.out.printf("\tAverage : %.2f\tGrade : %c", avg, grade);
    }
 
}
 
 cs

 

<ScoreManager.java>

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package quiz2.ex01.score;
 
import java.util.ArrayList;
 
public class ScoreManager_2 extends Score_2{
    
    ArrayList<Score_2> list = new ArrayList<Score_2>();
 
    public ScoreManager_2() {
        
    }
 
    public ScoreManager_2(String name, int kor, int eng, int com, int tot, double avg, char grade) {
        Score_2 s = new Score_2(name, kor, eng, com, tot, avg, grade);
        list.add(s);
    }
    
    //추가
    public void ScoreAdd(String name, int kor, int eng, int com, int tot, double avg, char grade) {
        Score_2 s = new Score_2(name, kor, eng, com, tot, avg, grade);
        list.add(s);
    }
    
    //삭제
    public void ScoreRmv(int i) {
        System.out.println("\n\n* 삭제된 학생");
        list.get(i-1).display(i);
        System.out.println("--------------");
        list.remove(i-1);
    }
    
    //수정->각각 수정하려면 필요없..음(main에서 실행가능)
//    public void ScoreCh(int i, String name, int kor, int eng, int com) {
//        Score_2 s = new Score_2(name, kor, eng, com);
//        list.set(i-1, s);
//    }
    
 
    
    //출력
    public void display(){
        System.out.println("저장된 학생 수 : " + list.size());
        for(int i=0; i<list.size(); i++){
            System.out.println();
            list.get(i).display(i);
        }// for
    }// display()
    
}// ScoreManaget_2 end
 
 cs

<Main.java>

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package quiz2.ex01.score;
 
//수정하기를 구체적으로 나누기 
import java.util.Scanner;
 
public class MainEntry_2 {
    static String name;
    static int kor;
    static int eng;
    static int com;
    static int tot;
    static double avg;
    static char grade;
 
    public static void main(String[] args) {
        ScoreManager_2 sm = new ScoreManager_2();
 
        Scanner sc = new Scanner(System.in);
        int edit_num;
 
        try {
            while (true) {
                System.out.println("\n\n*-*-*-*-* 메뉴 *-*-*-*-*");
                System.out.println("1. 학생 정보 입력");
                System.out.println("2. 학생 정보 삭제");
                System.out.println("3. 학생 정보 수정");
                System.out.println("4. 모든 학생 보기");
                System.out.println("5. 종료");
                System.out.println("----------------------");
                System.out.print(" >> ");
                int inNum = sc.nextInt();
 
                try {
                    switch (inNum) {
                    case 1:
                        System.out.println("\n*-*-*-* 1. 학생 정보 입력 *-*-*-*");
                        inScore();
                        sm.ScoreAdd(name, kor, eng, com, tot, avg, grade);
                        System.out.println("* 입력완료");
                        break;
                    case 2:
                        if(sm.list.isEmpty()) {
                            System.out.println("삭제할 학생이 없습니다.");
                            continue;
                        }
                        System.out.println("\n*-*-*-* 2. 학생 정보 삭제 *-*-*-*");
                        sm.display();
                        System.out.println("---------------------------");
                        System.out.print("삭제할 학생의 번호를 입력하세요 >> ");
                        inNum = sc.nextInt();
                        sm.ScoreRmv(inNum);
                        System.out.print("삭제되었습니다.");
                        break;
                    case 3:
                        if(sm.list.isEmpty()) {
                            System.out.println("수정할 학생이 없습니다.");
                            continue;
                        }
                        System.out.println("\n*-*-*-* 3. 학생 정보 수정 *-*-*-*");
                        sm.display();
                        System.out.println("---------------------------");
                        System.out.print("수정할 학생의 번호를 입력하세요 >> ");
                        inNum = sc.nextInt();
 
//                        do { //=>1)do ~ while 이용
                        while (true) { //=>2)while 이용
                            System.out.println("수정할 학생의 정보를 입력하세요.(1.이름, 2.국어점수, 3.영어점수, 4.전산점수)");
                            edit_num = sc.nextInt();
                            switch (edit_num) {
                            case 1: // 이름수정
//                                editName();
                                System.out.println("수정할 이름을 입력해주세요=>");
                                sm.list.get(inNum - 1).setName(sc.next());
                                System.out.println("수정되었습니다.");
//                                sm.ScoreCh(inNum, name, kor, eng, com); 
                                break;
                            case 2: // 국어점수 수정
                                System.out.println("국어점수를 입력해주세요=>");
                                sm.list.get(inNum - 1).setKor(sc.nextInt());
                                System.out.println("수정되었습니다.");
                                break;
                            case 3: // 영어점수 수정
                                System.out.println("영어점수를 입력해주세요=>");
                                sm.list.get(inNum - 1).setEng(sc.nextInt());
                                System.out.println("수정되었습니다.");
                                break;
                            case 4: // 전산점수 수정
                                System.out.println("전산점수를 입력해주세요=>");
                                sm.list.get(inNum - 1).setEng(sc.nextInt());
                                System.out.println("수정되었습니다.");
                                break;
                            default:
                                System.out.println("수정할 정보의 번호를 다시 입력해주세요.");
                                continue;
                            } // in switch end
 
                            System.out.println("계속 수정하시겠습니까?");
                            String con = sc.next();
                            if (con.equalsIgnoreCase("n")) {
                                break;
                            }
                        } //in while end
//                        } while (edit_num != 1 && edit_num != 2 && edit_num != 3 && edit_num != 4); // do while end
                        break;
                    case 4:
                        if(sm.list.isEmpty()) {
                            System.out.println("저장된 학생정보가 없습니다.");
                            continue;
                        }
                        System.out.println("\n*-*-*-* 4. 모든 학생 보기 *-*-*-*");
                        sm.display();
                        break;
                    case 5:
                        System.out.println("\n* 프로그램을 종료합니다.");
                        System.exit(0);
                        break;
                    default:
                        System.out.println("\nerr)잘못입력하셨습니다. 다시 입력해주세요.");
                    } // out switch end
                } catch (Exception e) {
                    System.out.println("err) 없는 학생입니다. 다시 입력해주세요.");
                } // try catch
            } // out while end
        } catch (Exception e) {
            System.out.println("err) 잘못 입력하셨습니다. 프로그램을 종료합니다.");
        } // try catch
 
    }
 
    public static void inScore() {
        Scanner sc = new Scanner(System.in);
 
        System.out.print("학생 이름을 입력해주세요: ");
        name = sc.next();
 
        do {
            System.out.println("학생의 국어점수를 입력하세요(0~100점사이값만 넣으세요) : ");
            kor = sc.nextInt();
        } while ((kor < 0) || (kor > 100));
 
        do {
            System.out.println("학생의 영어점수를 입력하세요(0~100점사이값만 넣으세요) : ");
            eng = sc.nextInt();
        } while ((eng < 0) || (eng > 100));
 
        do {
            System.out.println("학생의 전산점수를 입력하세요(0~100점사이값만 넣으세요) : ");
            com = sc.nextInt();
        } while ((com < 0) || (com > 100));
 
        process(name, kor, eng, com);
    }
 
    // 계산처리
    public static void process(String name, int kor, int eng, int com) {
 
        tot = kor + eng + com;
        avg = tot / 3.0;
 
        grade(avg);
    } // process end
 
    public static void grade(double avg) {
 
        if (avg <= 100 && avg > 90) {
            grade = 'A';
        } else if (avg <= 90 && avg > 80) {
            grade = 'B';
        } else if (avg <= 80 && avg > 70) {
            grade = 'C';
        } else if (avg <= 70 && avg > 60) {
            grade = 'D';
        } else
            grade = 'F';
    } // grade end
 
}
 
 cs

 

▶try ~ catch 문에서 catch는 여러개 쓸 수 있음

▶main메소드가 있는 클래스 안의 다른 메소드와 변수들은 접근지정자가 모두 main과 같은 static이여야만 함

 ->그래야 main메소드 안에서 불러오고 사용가능

▶while(true)와 do ~ while 모두 사용해봄 

 ->do ~ while은 while(조건)에서 조건에 맞는 상황에는 계속 실행: 여러 조건 넣을 때 ||와 && 혼동하지 않기

무한루프 안의 if문 안에서의 break; 무한루프 안의 switch문 안에서의 break;

while(true) {

     if문 ~~ {

        break; }} 
==>무한루프 탈출

while(true) {

     switch문~{

     case 1 : break; }}

==>switch문 탈출, while이 다시 반복 실행 

 

     

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▶BufferedReader의 readLine()을 이용한 연산 프로그램 

docs.oracle.com/javase/8/docs/api/

 

Java Platform SE 8

 

docs.oracle.com

<잘못된 코드>

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package quiz1.ex01.io;
 
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
 
//숫자 2개, 연산자 1개 입력받아서 사칙연산 프로그램 작성(io - BufferedReader)
public class MainEntry {
 
    public static void main(String[] args) throws IOException {
 
        String op = null;
        int su1 = 0, su2 = 0;
        double result = 0.;
 
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        try {
 
            while (true)
                second: {
                    System.out.println("숫자1을 입력하세요");
                    su1 = Integer.parseInt(br.readLine());
 
                    System.out.println("숫자2를 입력하세요.");
                    su2 = Integer.parseInt(br.readLine());
 
                    System.out.println("숫자1과 숫자2의 연산에 사용할 연산자를 고르세요.(+, -, *, /)");
                    op = br.readLine();
                    
                    switch (op) {
                    case "+":
                        result = su1 + su2;
                        break second;
                    case "-":
                        if (su1 >= su2) {
                            result = su1 - su2;
                        } else {
                            result = su2 - su1;
                        }
                        break second;
                    case "*":
                        result = su1 * su2;
                        break second;
                    case "/":
                        if (su1 >= su2) {
                            result = su1 / su2;
                        } else {
                            result = su2 / su1;
                        }
                        break second;
                    default: 
                        System.out.println("+,-,*,/ 중에 입력해주세요.");
                        continue;
                    
                    } // switch end
 
                } // while end
        } catch (Exception e) {
            e.printStackTrace();
        }
//==================!무한루프에서 빠져나오지 못함!==================ㅜㅜ
        if (su1 >= su2) {
            System.out.printf("%d %s %d = %.2f", su1, op, su2, result);
 
        } else {
            System.out.printf("%d %s %d = %.2f", su2, op, su1, result);
        }
    }// main end
}
 
 cs

-while(true)의 무한루프를 빠져나오지 못한다.

-while(true) second: { -> 식별자를 넣어

  break second;를 해도 while을 빠져나가는게 아니라, 다시 while문을 시작한다.

-default: 

     continue; 와 break; 와 아무것도 작성하지 않아도 모두 while문으로 돌아가 시작된다.

<완성한 코드>

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package quiz1.ex01.io;
 
import java.io.BufferedReader;
import java.io.InputStreamReader;
//숫자 2개, 연산자 1개 입력받아서 사칙연산 프로그램 작성(io - BufferedReader)
public class MainEntry2 {
    public static void main(String[] args) {
 
        String op = null;
        int su1 = 0, su2 = 0;
        double result = 0.;
 
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
 
        System.out.println("<<<<<operate program>>>>>");
        try {
            while (true) {
                System.out.println("숫자1을 입력하세요");
                su1 = Integer.parseInt(br.readLine());
 
                System.out.println("숫자2를 입력하세요.");
                su2 = Integer.parseInt(br.readLine());
 
                System.out.println("숫자1과 숫자2의 연산에 사용할 연산자를 고르세요.(+, -, *, /)");
                op = br.readLine();
 
                switch (op) {
                case "+":
                    result = su1 + su2;
                    break;
                case "-":
                    if (su1 >= su2) {
                        result = su1 - su2;
                    } else {
                        result = su2 - su1;
                    }
                    break;
                case "*":
                    result = su1 * su2;
                    break;
                case "/":
                    if (su1 >= su2) {
                        result = su1 / su2;
                    } else {
                        result = su2 / su1;
                    }
                    break;
                default:
                    System.out.println("연산자를 다시 입력해주세요");
                    continue;
                }// switch end
 
                if (su1 >= su2) {
                    System.out.printf("%d %s %d = %.2f", su1, op, su2, result);
 
                } else {
                    System.out.printf("%d %s %d = %.2f", su2, op, su1, result);
                }
 
                System.out.println("\n다시 입력하시겠습니까?");
                String re = br.readLine();
                if (re.equalsIgnoreCase("y")) {
                   continue; //==>안써도 다시 반복됨!!
                } else {
                    System.out.println("계산프로그램을 종료합니다.");
                    System.exit(0);
                }
                
            } // while end
        } catch (Exception e) {
            e.printStackTrace();
        } // try end
 
    }
 
}
 
 cs

-switch문 다음에 이어질 코드(출력과 재실행 유무)들을 모두 while(true)에 넣음

-switch문 안에서 작성한 break;가 실행되면 while(true)가 아니라, switch를 빠져나오게 됨

-default: continue;가 실행되면, 다시 while문의 처음으로 올라가서 반복실행됨

 

▶Unreachable code 에러

  Unreachable code란? 도달하지 않는 구문, 절대 실행될 수 없는 구문 

  In computer programming, unreachable code is part of the source code of a program which can never be executed because there exists no control flow path to the code from the rest of the program.[출처.위키백과]

en.wikipedia.org/wiki/Unreachable_code

 

Unreachable code - Wikipedia

From Wikipedia, the free encyclopedia Jump to navigation Jump to search In computer programming, unreachable code is part of the source code of a program which can never be executed because there exists no control flow path to the code from the rest of the

en.wikipedia.org

 

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