[JAVA] 25. 반복문 (2)구구단 하드코딩

1. 구구단 하드코딩 문제

2. 하드코딩해보기

package ex03;

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

        // 2단부터 9단까지 for문을 이용해 구구단을 만들어보자!
        // 절차를 잘 나누어봅시다.

        // 2단
        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");

        // 3단
        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");

        // 4단
        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");
				.
				.
				.
    }
}

3. 공통된 부분을 모듈화하기

1) 함수 적용1

package ex03;

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

        // 2단부터 9단까지 for문을 이용해 구구단을 만들어보자!
        // 절차를 잘 나누어봅시다.

				int a;
				
        // 2단
        a = 2;
        System.out.println(a + "*1=2");
        System.out.println(a + "*2=4");
        System.out.println(a + "*3=6");
        System.out.println(a + "*4=8");
        System.out.println(a + "*5=10");
        System.out.println(a + "*6=12");
        System.out.println(a + "*7=14");
        System.out.println(a + "*8=16");
        System.out.println(a + "*9=18");

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

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

2) 함수 적용2

package ex03;

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

        // 2단부터 9단까지 for문을 이용해 구구단을 만들어보자!
        // 절차를 잘 나누어봅시다.

				int a = 1;

        // 2단
        a = 2;
        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();

        // 3단
        a = 3;
        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();

        // 4단
        a = 4;
        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) for문 사용

package ex03;

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

        // 2단부터 9단까지 for문을 이용해 구구단을 만들어보자!
        // 절차를 잘 나누어봅시다.

				int a = 1;

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

        // 3단
        a = 3;
        for (int b = 1; b < 10; b++) {
            System.out.println(a + "*" + b + "=" + (a * b));
        }
        System.out.println();

        // 4단
        a = 4;
        for (int b = 1; b < 10; b++) {
            System.out.println(a + "*" + b + "=" + (a * b));
        }
        System.out.println();
        .
        .
        .
    }
}

4) 2중 for문 사용

package ex03;

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

        // 2단부터 9단까지 for문을 이용해 구구단을 만들어보자!
        // 절차를 잘 나누어봅시다.

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