[Java] 13. 2중 for문으로 구구단 만들기

Feb 04, 2025

Contents

1. 구구단 하드코딩

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// 1. 절차를 나눈다. // 2. 하드 코딩 한다. (노가다) - (패턴, 변수, 샘플링 가능해짐, 절차 생략할 수 있다 = given) // 3. 공통 모듈로 만든다. // 4. 불필요한 것들은 반복문으로 돌린다.

1. 하드코딩 STEP 1


package ex03;

public class Gugudan01 {
    public static void main(String[] args) {
        System.out.println("2*1=2");
        System.out.println("2*2=4");
        System.out.println("2*3=6");
        System.out.println("2*4=8");
        System.out.println("2*5=10");
        System.out.println("2*6=12");
        System.out.println("2*7=14");
        System.out.println("2*8=16");
        System.out.println("2*9=18");
        System.out.println();

        System.out.println("3*1=3");
        System.out.println("3*2=6");
        System.out.println("3*3=9");
        System.out.println("3*4=12");
        System.out.println("3*5=15");
        System.out.println("3*6=18");
        System.out.println("3*7=21");
        System.out.println("3*8=24");
        System.out.println("3*9=27");
        System.out.println();

        System.out.println("4*1=4");
        System.out.println("4*2=8");
        System.out.println("4*3=12");
        System.out.println("4*4=16");
        System.out.println("4*5=20");
        System.out.println("4*6=24");
        System.out.println("4*7=28");
        System.out.println("4*8=32");
        System.out.println("4*9=36");
        System.out.println();
    }
}

2. 공통모듈 만들기 STEP 2


package ex03;

public class Gugudan01 {
    public static void main(String[] args) {

        int a = 1;

        // 1. 2단
        a++;
        System.out.println(a + "*" + 1 + "=" + (a * 1));
        System.out.println(a + "*" + 2 + "=" + (a * 2));
        System.out.println(a + "*" + 3 + "=" + (a * 3));
        System.out.println(a + "*" + 4 + "=" + (a * 4));
        System.out.println(a + "*" + 5 + "=" + (a * 5));
        System.out.println(a + "*" + 6 + "=" + (a * 6));
        System.out.println(a + "*" + 7 + "=" + (a * 7));
        System.out.println(a + "*" + 8 + "=" + (a * 8));
        System.out.println(a + "*" + 9 + "=" + (a * 9));
        System.out.println();

        // 2. 3단
        a++;
        System.out.println(a + "*" + 1 + "=" + (a * 1));
        System.out.println(a + "*" + 2 + "=" + (a * 2));
        System.out.println(a + "*" + 3 + "=" + (a * 3));
        System.out.println(a + "*" + 4 + "=" + (a * 4));
        System.out.println(a + "*" + 5 + "=" + (a * 5));
        System.out.println(a + "*" + 6 + "=" + (a * 6));
        System.out.println(a + "*" + 7 + "=" + (a * 7));
        System.out.println(a + "*" + 8 + "=" + (a * 8));
        System.out.println(a + "*" + 9 + "=" + (a * 9));
        System.out.println();

        // 3. 4단
        a++;
        System.out.println(a + "*" + 1 + "=" + (a * 1));
        System.out.println(a + "*" + 2 + "=" + (a * 2));
        System.out.println(a + "*" + 3 + "=" + (a * 3));
        System.out.println(a + "*" + 4 + "=" + (a * 4));
        System.out.println(a + "*" + 5 + "=" + (a * 5));
        System.out.println(a + "*" + 6 + "=" + (a * 6));
        System.out.println(a + "*" + 7 + "=" + (a * 7));
        System.out.println(a + "*" + 8 + "=" + (a * 8));
        System.out.println(a + "*" + 9 + "=" + (a * 9));
        System.out.println();
    }
}

3. 반복시키기 (9바퀴 돌면 됨)


package ex03;

public class Gugudan01 {
    public static void main(String[] args) {

        int a = 1;
        
        for (int i = 0; i < 8; i++) {
            a++;
            System.out.println(a + "*" + 1 + "=" + (a * 1));
            System.out.println(a + "*" + 2 + "=" + (a * 2));
            System.out.println(a + "*" + 3 + "=" + (a * 3));
            System.out.println(a + "*" + 4 + "=" + (a * 4));
            System.out.println(a + "*" + 5 + "=" + (a * 5));
            System.out.println(a + "*" + 6 + "=" + (a * 6));
            System.out.println(a + "*" + 7 + "=" + (a * 7));
            System.out.println(a + "*" + 8 + "=" + (a * 8));
            System.out.println(a + "*" + 9 + "=" + (a * 9));
            System.out.println();
        }


    }
}

2. (최종) 구구단 만들기


package ex03;

public class Gugudan01 {
    public static void main(String[] args) {

        for (int a = 2; a < 10; a++) {
            for (int b = 1; b < 10; b++) {
                System.out.println(a + " * " + b + " = " + (a * b));
            }
            System.out.println();
        }
    }
}