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 + "!");
}
}

11import 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);}}12import java.util.Scanner;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.");elseSystem.out.println(hexs[(int)(hex.charAt(0) - 'A' + 10)]);}}13import 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");elseSystem.out.println(ch + " is a invalid input");}}14import 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')]);elseSystem.out.println(alpha + " is an invalid grade");}}15import 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;}}}elseSystem.out.println(letter + " is an invalid input");}}16import java.util.Scanner;public class Main {public static void main(String[] args) {int num = (int)(Math.random()*26);System.out.println((char)(num+'A'));}}17import 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