[JAVA] 14. 구구단 만들기

1. 하드코딩 STEP 1

package ex03;

public class Gugudan01 {
    public static void main(String[] args) {
        System.out.println("2*1=2"); // 변수 * 1 = (변수 * 1)
        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();
    }
}

• 변수를 찾아 변수 값 초기화 및 변수가 증가하는 함수 추가

• 모든 단 똑같이 만들기 (공통 모듈 만들기)

3. for문 사용하여 반복시키기 (9바퀴)

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();
        }
    }
}

• for문 이용해서 모든 단을 하나로 묶기

최종 코드

package ex03;

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

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