Chapter 03 실습문제

1번

1) 425

2)

public class ex3_1 {
	public static void main(String[] args) {
		int sum=0,i=1;
		while(true) {
			if(i>50) {
				break;
			}
			sum+=i;
			i+=3;
		}
		System.out.print(sum);
	}
}

 

3) 

public class ex3_1 {
	public static void main(String[] args) {
		int sum=0,i=1;
		for(i=1;i<50;i+=3) {
			sum+=i;
		}
		System.out.print(sum);
	}
}

4)

public class ex3_1 {
	public static void main(String[] args) {
		int sum=0,i=1;
		do {
			sum+=i;
			i+=3;
		}while(i<50);
		System.out.print(sum);
	}
}

2번

1) 20 72 256

2)

public class ex3_2 {
	public static void main(String[] args) {
		int n[]= {1,-2,6,20,5,72,-16,256};
		for(int i=0; i<n.length;i++) {
			if(n[i]>0&&n[i]%4==0) {
				System.out.print(n[i]+" ");
			}
		}
	}
}

3)

public class ex3_2 {
	public static void main(String[] args) {
		int n[]= {1,-2,6,20,5,72,-16,256};
		int i=0;
		while(true) {
			if(n[i]>0&&n[i]%4==0) {
				System.out.print(n[i]+" ");
			}
			i++;
			if(i>=n.length) {
				break;
			}
		}
	}
}

4)

public class ex3_2 {
	public static void main(String[] args) {
		int n[]= {1,-2,6,20,5,72,-16,256};
		int i=0;
		do{
			if(n[i]>0&&n[i]%4==0) {
				System.out.print(n[i]+" ");
			}
			i++;
		}while(i<n.length);
	}
}

3번

import java.util.Scanner;
public class ex3_3 {
	public static void main(String[] args) {
		Scanner scanner=new Scanner(System.in);
		
		while(true) {
			System.out.print("양의 정수 입력>>");
			int N=scanner.nextInt();
			if(N>0) {
				for(int i=0;i<N;i++) {
					for(int j=i;j<N;j++) {
						System.out.print("*");
					}
					System.out.println();
				}
				break;
			}
		}
		scanner.close();
	}
}

4번

public class ex3_4 {
	public static void main(String[] args) {
		int n[][]=new int[5][];
		n[0]=new int[3];
		n[1]=new int[2];
		n[2]=new int[1];
		n[3]=new int[3];
		n[4]=new int[4];
		
		for(int i=0;i<n.length;i++) {
			for(int j=0;j<n[i].length;j++) {
				n[i][j]=j+1;
			}
		}
		
		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();
		}
	}
}

5번

import java.util.Scanner;
public class ex3_5 {
	public static void main(String[] args) {
		System.out.print("양의 정수 10개 입력>>");
		Scanner scanner=new Scanner(System.in);
		int n[]=new int[10];
		for(int i=0;i<10;i++) {
			n[i]=scanner.nextInt();
		}
		System.out.print("3의 배수는...");
		for(int i=0;i<10;i++) {
			if(n[i]%3==0) {
				System.out.print(n[i]+" ");
			}
		}
		scanner.close();
	}
}

6번

import java.util.Scanner;
public class ex3_6 {
	public static void main(String[] args) {
		System.out.print("양의 정수 10개 입력>>");
		Scanner scanner=new Scanner(System.in);
		int n[]=new int[10];
		int n_copy[]=new int[10];
		for(int i=0;i<10;i++) {
			n[i]=scanner.nextInt();
			n_copy[i]=n[i];
		}
		
		System.out.print("자리수의 합이 9인 것은...");
		int sum[]=new int[10];
		for(int i=0;i<10;i++) {
			while (n[i] > 0) {
	            sum[i] += n[i] % 10; 
	            n[i] /= 10;       
	        }
		}
		for(int i=0;i<10;i++) {
			if(sum[i]==9) {
				System.out.print(n_copy[i]+" ");
			}
		}
		scanner.close();
	}
}

7번

import java.util.Random;

public class ex3_7 {
	public static void main(String[] args) {
		int array[]=new int[10];
		Random random = new Random();
		int sum=0;
		System.out.print("랜덤한 정수들 ...");
		for(int i=0;i<10;i++) {
			array[i]=random.nextInt(9)+11;
			System.out.print(array[i]+" ");
			sum+=array[i];
		}
		System.out.println();
		double average=(double)(sum/10);
		System.out.print("평균은 "+average);
	}
}

8번

import java.util.Scanner;
import java.util.Random;
public class ex3_8 {
	public static void main(String[] args){
		Scanner scanner=new Scanner(System.in);
		System.out.print("정수 몇 개 저장하시겠습니까?>>");
		int array[]=new int[scanner.nextInt()];
		Random random=new Random();
		System.out.print("랜덤한 정수들...");
		int sum=0;
		for(int i=0;i<array.length;i++) {
			array[i]=random.nextInt(100)+1;
			System.out.print(array[i]+" ");
			sum+=array[i];
		}
		System.out.println();
		double average=(double)(sum/array.length);
		System.out.print("평균은 "+average);
		scanner.close();
	}
}

10번

import java.util.Random;
import java.util.Scanner;
public class ex3_11 {
	public static void main(String[] args) {
		System.out.println("4X4 배열에 랜덤한 값을 저장한 후 출력합니다.");
		Scanner scanner=new Scanner(System.in);
		Random random=new Random();
		int array[][]=new int[4][4];
		for(int i=0;i<4;i++) {
			for(int j=0;j<4;j++) {
				array[i][j]=random.nextInt(255);
			}
		}
		
		for(int i=0;i<4;i++) {
			for(int j=0;j<4;j++) {
				System.out.print(array[i][j]+"\t");
			}
			System.out.println();
		}
		System.out.print("임계값 입력>>");
		int number=scanner.nextInt();
		for(int i=0;i<4;i++) {
			for(int j=0;j<4;j++) {
				if(array[i][j]>number) {
					array[i][j]=255;
				}
				else {
					array[i][j]=0;
				}
			}
		}
		
		for(int i=0;i<4;i++) {
			for(int j=0;j<4;j++) {
				System.out.print(array[i][j]+"\t");
			}
			System.out.println();
		}
	}
}

11번

import java.util.Random;
import java.util.Scanner;
public class ex3_11 {
	public static void main(String[] args) {
		Random random=new Random();
		Scanner scanner=new Scanner(System.in);
		System.out.println("***** 구구단을 맞추는 퀴즈입니다. *****");
		int count=0;
		do {
			int number1=random.nextInt(9)+1;
			int number2=random.nextInt(9)+1;
			System.out.printf("%d * %d = ",number1,number2);
			int answer=scanner.nextInt();
			if(answer==number1*number2) {
				System.out.println("맞았습니다.");
			}
			else {
				count++;
				System.out.printf("%d번 틀렸습니다. 분발하세요.\n",count);
			}
		}while(count<3);
		scanner.close();
	}
}