java语言程序设计基础篇第四章编程练习题

1

import java.util.Scanner;
public class Main{
	public static void main(String[] args){
		Scanner input = new Scanner(System.in);
		double r = input.nextDouble();
		double s = 2*r*Math.sin(Math.PI/5);
		double area  = (5*Math.pow(s, 2))/(4*Math.tan(Math.PI/5));
		System.out.println(area);
	}
}

2

import java.util.Scanner;
public class Main{
	public static void main(String[] args){
		Scanner input = new Scanner(System.in);
		double R = 6371.01;
		double x1 = input.nextDouble();
		x1 = Math.toRadians(x1);
		double y1 = input.nextDouble();
		y1 = Math.toRadians(y1);
		double x2 = input.nextDouble();
		x2 = Math.toRadians(x2);
		double y2 = input.nextDouble();
		y2 = Math.toRadians(y2);
		double distance = R*Math.acos(Math.sin(x1)*Math.sin(x2) + Math.cos(x1)*Math.cos(x2)*Math.cos(y1-y2));
		System.out.println(distance);
	}
}

3

这是个悲剧，给出的地图网址打不开，虽然百度地图也可以找到，但是我可真不想去美国地图上找城市，还要算经纬度，直接放弃这题了。

4

import java.util.Scanner;
public class Main {

	public static void main(String[] args) {
		Scanner input = new Scanner(System.in);
		System.out.print("Enter the side:");
		double side = input.nextDouble();
		double s = (6*side*side)/(4*Math.tan(Math.PI/6));
		System.out.println("The area of the hexagon is " + s);
	}
}

5

书上的公式给错了，正确公式：面积 = (n*s*s)/(4*tan(π/n))
import java.util.Scanner;
public class Main {

	public static void main(String[] args) {
		Scanner input = new Scanner(System.in);
		System.out.print("Enter the number of sides:");
		int numberOfTheSide = input.nextInt();
		System.out.print("Enter the sides:");
		double side = input.nextDouble();
		double s = (numberOfTheSide*side*side)/(4*Math.tan(Math.PI/numberOfTheSide));
		System.out.println("The area of the ploygon is " + s);
	}
}

6

import java.util.Scanner;
public class Main {

	public static void main(String[] args) {
		double radius = 40.0;
		double radians = Math.random()*Math.PI*2;
		double x1 = radius * Math.cos(radians);
		double y1 = radius * Math.sin(radians);
		
		radians = Math.random()*Math.PI*2;
		double x2 = radius * Math.cos(radians);
		double y2 = radius * Math.sin(radians);
		
		radians = Math.random()*Math.PI*2;
		double x3 = radius * Math.cos(radians);
		double y3 = radius * Math.sin(radians);
		
		double sideA = Math.sqrt(Math.pow(x1-x2,2.0) + Math.pow(y1-y2, 2.0));
		double sideB = Math.sqrt(Math.pow(x1-x3,2.0) + Math.pow(y1-y3, 2.0));
		double sideC = Math.sqrt(Math.pow(x3-x2,2.0) + Math.pow(y3-y2, 2.0));
		
		double cosA = (sideB*sideB + sideC*sideC - sideA*sideA)/(2*sideB*sideC);
		double cosB = (sideA*sideA + sideC*sideC - sideB*sideB)/(2*sideA*sideC);
		double cosC = (sideB*sideB + sideA*sideA - sideC*sideC)/(2*sideB*sideA);
		
		System.out.println("cosA: " + Math.toDegrees(Math.acos(cosA)));
		System.out.println("cosB: " + Math.toDegrees(Math.acos(cosB)));
		System.out.println("cosC: " + Math.toDegrees(Math.acos(cosC)));
	}
}

7

import java.util.Scanner;
public class Main {
	
	public static void main(String[] args){
		Scanner cin = new Scanner(System.in);
		double oneDegree = Math.PI/180;
		System.out.print("Enter the radius of the bounding circle:");
		double radius = cin.nextDouble();
		System.out.println("The coordinating of five points on the pentagon are");
		//y轴上那个点
		System.out.println("(" + 0 + "," + radius + ")");
		double x = Math.sqrt((radius*radius)/(1+Math.tan(18*oneDegree)*Math.tan(18*oneDegree)));
		double y = x*Math.tan(18*oneDegree);
		System.out.println("(" + x + "," + y + ")");
		System.out.println("(" + -x + "," + y + ")");
		x = Math.sqrt((radius*radius)/(1+Math.tan(54*oneDegree)*Math.tan(54*oneDegree)));
		y = x*Math.tan(54*oneDegree);
		System.out.println("(" + x + "," + y + ")");
		System.out.println("(" + -x + "," + y + ")");
	}
}

8

import java.util.Scanner;
public class Main {

	public static void main(String[] args) {
		Scanner input = new Scanner(System.in);
		System.out.print("Enter an ACSII code:");
		byte num = input.nextByte();
		char c = (char)num;
		System.out.println("The character for ACSII code " + num + " is " + c);
	}
}

9

import java.util.Scanner;
public class Main {

	public static void main(String[] args) {
		Scanner input = new Scanner(System.in);
		System.out.print("Enter a charater:");
		String s = input.nextLine();
		char c = s.charAt(0);
		int num = (int)c;
		System.out.println("The Unicode for the character " + c + " is " + num);
	}
}

10

import java.util.Scanner;
public class Main {

	public static void main(String[] args) {
		String set1 = 
			" 1  3  5  7\n"+
			" 9 11 13 15\n"+
			"17 19 21 23\n"+
			"25 27 29 31";
		
		String set2 = 
				" 2  3  6  7\n"+
				"10 11 14 15\n"+
				"18 19 22 23\n"+
				"26 27 30 31";
		
		String set3 = 
				" 4  5  6  7\n"+
				"12 13 14 15\n"+
				"20 21 22 23\n"+
				"28 29 30 31";
		
		String set4 = 
				" 8  9 10 11\n"+
				"12 13 14 15\n"+
				"24 25 26 27\n"+
				"28 29 30 31";
		
		String set5 = 
				"16 17 18 19\n"+
				"20 21 22 23\n"+
				"24 25 26 27\n"+
				"28 29 30 31";
		
		int day = 0;
		Scanner input = new Scanner(System.in);
		
		System.out.println("Is your birthday in set1?");
		System.out.print(set1);
		System.out.print("\nEnter N for No and Y for Yes:");
		String s = input.nextLine();
		
		if(s.charAt(0) == 'Y')
			++day;
		
		System.out.println("Is your birthday in set2?");
		System.out.print(set2);
		System.out.print("\nEnter N for No and Y for Yes:");
		s = input.nextLine();
		
		if(s.charAt(0) == 'Y')
			day += 2;
		
		System.out.println("Is your birthday in set3?");
		System.out.print(set3);
		System.out.print("\nEnter N for No and Y for Yes:");
		s = input.nextLine();
		
		if(s.charAt(0) == 'Y')
			day += 4;
		
		System.out.println("Is your birthday in set4?");
		System.out.print(set4);
		System.out.print("\nEnter N for No and Y for Yes:");
		s = input.nextLine();
		
		if(s.charAt(0) == 'Y')
			day += 8;
		
		System.out.println("Is your birthday in set5?");
		System.out.print(set5);
		System.out.print("\nEnter N for No and Y for Yes:");
		s = input.nextLine();
		
		if(s.charAt(0) == 'Y')
			day += 16;
		
		System.out.println("\nYour birthday is " + day + "!");
	}
}

11

import java.util.Scanner;
public class Main {

	public static void main(String[] args) {
		System.out.print("Enter a decimal value(0 to 15):");
		Scanner input = new Scanner(System.in);
		int num = input.nextInt();
		char ch = (char)num;
		char hex = (char)(ch + 'A' - 10);
		System.out.println("The hex value is " + hex);
	}
}

12

import java.util.*;

public class Main {

    public static void main(String[] args) {
        String[] hexs = {"0000", "0001", "0010", "0011", "0100", "0101",
                "0110", "0111", "1000", "1001", "1010", "1011", "1100", "1101",
                "1110", "1111"};
        Scanner input = new Scanner(System.in);
        String hex = input.nextLine();
        if (hex.charAt(0) > 'F' || hex.charAt(0) < '0')
            System.out.println(hex.charAt(0) + " is an invalid input.");
        else {
            char ch = hex.charAt(0);
            if(ch >= 'A' && ch <= 'F')
                System.out.println(hexs[(int)(hex.charAt(0) - 'A' + 10)]);
            else
                System.out.println(hexs[(int)(ch-'0')]);
        }
    }

}

13

import java.util.Scanner;
public class Main {

	public static void main(String[] args) {
		Scanner input = new Scanner(System.in);
		System.out.print("Enter a letter:");
		String alpha = input.nextLine();
		char ch = alpha.charAt(0);
		if(ch == 'A' || ch == 'E' || ch == 'I' || ch == 'O' || ch == 'U'
			|| ch == 'a' || ch == 'e' || ch == 'i' || ch == 'o' || ch == 'u' )
			System.out.println(ch + " is a vowel");
		else if(Character.isLetter(ch))
			System.out.println(ch + " is a consonant");
		else
			System.out.println(ch + " is a invalid input");
	}
}

14

import java.util.Scanner;
public class Main {

	public static void main(String[] args) {
		int[] grades = {4,3,2,1,0,0};
		Scanner input = new Scanner(System.in);
		System.out.print("Enter a letter grade:");
		String letter = input.nextLine();
		char alpha = letter.charAt(0);
		if(alpha == 'A' || alpha == 'B' || alpha == 'C' || alpha == 'D' || alpha == 'F')
			System.out.println("The numeric value for grade " + alpha + " is " + grades[(int)(alpha-'A')]);
		else
			System.out.println(alpha + " is an invalid grade");
	}
}

15

import java.util.Scanner;
public class Main {

	public static void main(String[] args) {
		String[] key = {"abcABC","defDEF","ghiGHI","jklJKL","mnoMNO",
				"pqrsPQRS","tuvTUV","wxyzWXYZ"};
		Scanner input = new Scanner(System.in);
		System.out.print("Enter a letter:");
		String letters = input.nextLine();
		char letter = letters.charAt(0);
		if(Character.isLetter(letter)){
			for(int i = 0; i < 8; ++i){
				if(key[i].indexOf(letter) != -1){
					System.out.println("The corresponding number is " + (i+2));
					break;
				}
			}
		}
		else
			System.out.println(letter + " is an invalid input");
	}
}

16

import java.util.Scanner;
public class Main {

	public static void main(String[] args) {
		int num = (int)(Math.random()*26);
		System.out.println((char)(num+'A'));
	}
}

17

import java.util.Scanner;
public class Main {

	public static void main(String[] args) {
		String[] months = {"Jan","Feb","Mar","Apr","May","Jun","Jul","Aug","Sep","Oct","Nov","Dec"};
		int[] dayOfMonth = {31,28,31,30,31,30,31,31,30,31,30,31};
		Scanner input = new Scanner(System.in);
		System.out.print("Enter a year:");
		int year = input.nextInt();
		System.out.print("Enter a month:");
		//吃回车的
		String temp = input.nextLine();
		
		String month = input.nextLine();
		int days = 0;
		for(int i = 0; i < 12; ++i)
			if(months[i].equals(month)){
				days = dayOfMonth[i];
				break;
			}
		if(month.equals("Feb")){
			if((year%400 == 0) || (year%4 == 0 && year%100 != 0))
				++days;
		}
		System.out.println(month + " " + year + " has " + days + " days");
	}
}

18

import java.util.Scanner;

public class Main{
	public static void main(String[] args){
		Scanner input = new Scanner(System.in);
		System.out.print("Enter two characters:");
		String str = input.nextLine();
		char ch = str.charAt(0);
		int num = Integer.parseInt((str.charAt(1)+""));
		if(ch != 'M' && ch != 'C' && ch != 'I'){
			System.out.println("Invalid input");
			return ;
		}
		if(num < 1 || num > 4){
			System.out.println("Invalid input");
			return ;
		}
		int flag = 0;
		if(ch == 'M' && num == 1){
			System.out.print("Mathematics ");
			flag = 1;
		}
		else if(ch == 'C' && num == 1){
			System.out.print("Computer Science ");
			flag = 1;
		}
		else if(ch == 'I' && num == 1){
			System.out.print("Information Technology ");
			flag = 1;
		}
		if(flag == 1){
			System.out.println("Freshman");
			return ;
		}
		
		if(ch == 'M')
			System.out.print("Mathematics ");
		else if(ch == 'C')
			System.out.print("Computer Science ");
		else if(ch == 'I')
			System.out.print("Information Technology ");
		System.out.println("Junior");
	}
}

19

编程练习题3.9，字符转数字

20

import java.util.Scanner;

public class Main{
	public static void main(String[] args){
		Scanner input = new Scanner(System.in);
		System.out.print("Enter a string:");
		String str = input.nextLine();
		System.out.println("length:" + str.length() + "\n" + "The first character:" + str.charAt(0));
	}
}

21

import java.util.Scanner;

public class Main{
	public static void main(String[] args){
		Scanner input = new Scanner(System.in);
		System.out.print("Enter a SSN:");
		String str = input.nextLine();
		if(str.indexOf('-') == 3 && str.lastIndexOf('-') == 6){
			System.out.println(str + " is a valid social security number");
		}
		else
			System.out.println(str + " is an ivalid social security number");
	}
}

22

import java.util.Scanner;

public class Main{
	public static void main(String[] args){
		Scanner input = new Scanner(System.in);
		System.out.print("Enter string s1:");
		String str1 = input.nextLine();
		System.out.print("Enter string s2:");
		String str2 = input.nextLine();
		if(str1.indexOf(str2) != -1){
			System.out.println(str2 + " is a substring of " + str1);
		}
		else
			System.out.println(str2 + " is not a substring of " + str1);
	}
}

23

。。。。。

24

import java.util.Scanner;

public class Main{
	public static void main(String[] args){
		Scanner input = new Scanner(System.in);
		System.out.print("Enter the first city:");
		String city1 = input.nextLine();
		System.out.print("Enter the second city:");
		String city2 = input.nextLine();
		System.out.print("Enter the third city:");
		String city3 = input.nextLine();
		String temp = null;
		if(city1.compareTo(city2) < 0){
			temp = city1;
			city1 = city2;
			city2 = temp;
		}
		
		if(city1.compareTo(city3) < 0){
			temp = city1;
			city1 = city3;
			city3 = temp;
		}
		
		if(city2.compareTo(city3) < 0){
			temp = city2;
			city2 = city3;
			city3 = temp;
		}
		
		System.out.print(city1 + "\n" + city2 + "\n" + city3);
	}
}

25

import java.util.Scanner;

public class Main{
	public static void main(String[] args){
		char ch1 = (char)((int)(Math.random()*26) + 'A');
		char ch2 = (char)((int)(Math.random()*26) + 'A');
		char ch3 = (char)((int)(Math.random()*26) + 'A');
		String num = ch1 + "" + ch2 + "" + ch3 + "" + (int)(Math.random()*10) + "" 
		+ (int)(Math.random()*10) + "" + (int)(Math.random()*10) + "" + (int)(Math.random()*10);
		System.out.println(num);
	}
}

26

indexOf定位，substring提取