명품 JAVA 3장 실습문제

prac 3_1_1
0부터 99까지 2씩 증가하면서 모든 수를 더하는 코드/ 실행 결과: 2450

prac 3_1_2
public class WhileTest {
	public static void main(String[] args) {
		int sum = 0, i = 0;
		while ( i < 100) {
			sum += i;
			i +=2;
		}
		System.out.println(sum);
	}
}

prac 3_1_3
public class ForTest {
	public static void main(String[] args) {
		int sum = 0;
		for (int i = 0; i < 100; i+=2) {
			sum += i;
		}
		System.out.println(sum);
	}
}

prac 3_1_4
public class DoWhileTest {
	public static void main(String[] args) {
		int sum = 0, i = 0;
		do {
			sum += i;
			i +=2;
		} while (i < 100);
		System.out.println(sum);
	}
}

prac 3_2

public class prac2 {
	public static void main(String[] args) {
		int n [][] = { {1}, {1,2,3}, {1}, {1,2,3,4}, {1,2}};
		for (int i = 0; i< n.length; i++) {
			for (int j = 0; j < n[i].length; j++)
				System.out.print(n[i][j] + " ");
			System.out.println();
		}
	}
}

prac 3_3

import java.util.*;

public class prac2 {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		System.out.print("정수를 입력하시오>>");
		int n = sc.nextInt();

		for (int i = n; i >= 1; i--) {
			for (int j = 0; j < i; j++)
				System.out.print("*");
			System.out.println();
		}
		sc.close();
	}
}

prac 3_4

import java.util.*;

public class prac2 {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		System.out.print("소문자 알파벳 하나를 입력하시오>>");
		String s = sc.next();
		char c = s.charAt(0);

		for (int i = 0; i <= c - 'a'; i++) {
			for (char j = 'a'; j <= c - i; j++)
				System.out.print(j);
			System.out.println();
		}
		sc.close();
	}
}

prac 3_5

import java.util.*;

public class prac2 {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int[] arr = new int[10];

		System.out.print("양의 정수 10개를 입력하시오>>");
		for (int i = 0; i < arr.length; i++) {
			arr[i] = sc.nextInt();
			if (arr[i] % 3 == 0)
				System.out.print(arr[i] + " ");
		}
		sc.close();
	}
}

prac 3_6

import java.util.*;

public class prac2 {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int[] unit = { 50000, 10000, 1000, 500, 100, 50, 10, 1 };

		System.out.print("금액을 입력하시오>>");
		int money = sc.nextInt();

		for (int i = 0; i < unit.length; i++) {
			if (money / unit[i] != 0) {
				System.out.println(unit[i] + "원 짜리 : " + money / unit[i] + "개");
				money %= unit[i];
			}
		}
		sc.close();
	}
}

prac 3_7

public class prac2 {
	public static void main(String[] args) {
		int[] arr = new int[10];
		int sum = 0;
		
		System.out.print("랜덤한 정수들: ");
		
		for (int i = 0; i < arr.length; i++) {
			arr[i] = (int) (Math.random() * 10 + 1);
			sum += arr[i];
			System.out.print(arr[i] + " ");
		}
		
		System.out.println("\n평균은 " + (double) sum / arr.length);
	}
}

prac 3_8

import java.util.*;

public class prac2 {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		System.out.print("정수 몇개? ");
		int n = sc.nextInt();
		int[] arr = new int[n];

		for (int i = 0; i < arr.length; i++) {
			arr[i] = (int) (Math.random() * 100 + 1);
			System.out.print(arr[i] + " ");
		}
		System.out.println();
	}
}

prac 3_9

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

		int[][] arr = new int[4][4];

		for (int i = 0; i < arr.length; i++) {
			for (int j = 0; j < arr.length; j++)
				arr[i][j] = (int) (Math.random() * 10 + 1);
		}

		for (int i = 0; i < arr.length; i++) {
			for (int j = 0; j < arr.length; j++)
				System.out.print(arr[i][j] + " ");
			System.out.println();
		}

	}
}

prac 3_10

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

		int arr[][] = new int[4][4];
		int x, y, result = 0;

		while (result < 10) {
			x = (int) (Math.random() * 4);
			y = (int) (Math.random() * 4);
			if (arr[x][y] == 0) {
				arr[x][y] = (int) (Math.random() * 10 + 1);
				result++;
			}
		}
		for (int i = 0; i < arr.length; i++) {
			for (int j = 0; j < arr.length; j++)
				System.out.print(arr[i][j] + " ");
			System.out.println();
		}

	}
}

prac 3_11

import java.util.*;

public class JavaPrac {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int sum = 0;

		for (int i = 0; i < 3; i++)
			sum += Integer.parseInt(args[i]);
		System.out.println(sum / 3);
		sc.close();
	}
}

prac 3_12

import java.util.*; 

public class JavaPrac {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int sum = 0;

		for (int i = 0; i < args.length; i++) {
			try {
				sum += Integer.parseInt(args[i]);
			} catch(Exception e) {
				continue;
			}
		}
		System.out.println("합: " + sum);
		sc.close();
	}
}

prac 3_13

public class JavaPrac {
	public static void main(String[] args) {
		for (int i = 1; i < 100; i++) {
			int a = i % 10;
			int b = i / 10;

			if ((a == 3 || a == 6 || a == 9) && (b == 3 || b == 6 || b == 9))
				System.out.println(i + " 박수 짝짝");
			else if (a == 3 || a == 6 || a == 9 || b == 3 || b == 6 || b == 9)
				System.out.println((i + " 박수 짝"));
		}
	}
}