C4 数学函数、字符和字符串
修改彩票程序
输入产生两位随机字符串代替数字，使用字符串接受用户的输入
import java.util.*;
public class test {
public static void main(String[] args) {
String lottery = "" + (int)(Math.random()* 10)
+ (int)(Math.random()* 10);
Scanner input = new Scanner(System.in);
System.out.print("Enter your lottery pick (two digits):");
String guess = input.nextLine();
char lotteryD1 = lottery.charAt(0);
char lotteryD2 = lottery.charAt(1);
char guessD1 = guess.charAt(0);
char guessD2 = guess.charAt(1);
System.out.println("The lottery number is " + lottery);
if (guess.equals(lottery))
System.out.println("Exact match: you win $10,000");
else if((lotteryD1 == guessD2)
&& (lotteryD2 == guessD1)) {
System.out.println("Match all digits,you win $3000 " );
}
else if((lotteryD1 == guessD1)
|| (lotteryD1 == guessD2)
|| (lotteryD2 == guessD1)
|| (lotteryD2 == guessD2)) {
System.out.println("Match all digits,you win $1000 " );
}
else
System.out.println("sorry no match " );
}
}
//Enter your lottery pick (two digits):00
//The lottery number is 59
//sorry no match
4.5 几何：正多边形的面积
正多边形是一个具有n条边的多边形，它每条边的长度都相等，而且所有角的度数也相等（即多边形既等边又等角）。
这里，s是边长。编写一个程序，提示用户输入边的个数以及正多边形的边长，然后显示它的面积。
import java.util.*;
public class test {
public static void main(String[] args) {
int numberOfSide;
double area, side;
System.out.print("Enter the number of sides:");
Scanner input = new Scanner(System.in);
numberOfSide = input.nextInt();
System.out.print("Enter the side；");
side = input.nextDouble();
area = (numberOfSide * Math.pow(side, 2)) / (4 * Math.tan(Math.PI / numberOfSide));
System.out.printf("The area of the hexagon is %5.4f", area);
input.close();
}
}
//Enter the number of sides:6
//Enter the side；6
//The area of the hexadon is 93.5307
4.21 检查 SSN
编写一个程序，提示用户输入一个社保号码，它的格式是DDD-DD-DDDD，其中D是一个数字。你的程序应该判断输入是否合法。
下面是一个运行示例：
Enter a SSN: 232-23-5435
232-23-5435 is a valid social security number
Enter a SSN: 23-23-5435
23-23-5435 is an invalid social security number
import java.util.*;
public class test {
public static void main(String[] args) {
System.out.print("Enter a SSN: ");
Scanner input = new Scanner(System.in);
String ssnString = input.nextLine();
if (ssnString.length() == 11)
{
if (Character.isDigit(ssnString.charAt(0))
&& Character.isDigit(ssnString.charAt(1))
&& Character.isDigit(ssnString.charAt(2))
&& ssnString.charAt(3) == '-'
&& Character.isDigit(ssnString.charAt(4))
&& Character.isDigit(ssnString.charAt(5))
&& ssnString.charAt(6) == '-'
&& Character.isDigit(ssnString.charAt(7))
&& Character.isDigit(ssnString.charAt(8))
&& Character.isDigit(ssnString.charAt(9))
&& Character.isDigit(ssnString.charAt(10)))
System.out.println(ssnString + " is a valid social security number");
else
System.out.println(ssnString + " is an invalid social security number");
}
else
System.out.println(ssnString + "is an invalid social security number");
input.close();
}
}
//Enter a SSN: 123-45-6666
//123-45-6666 is a valid social security number
4.26 金融应用：货币单位
重写程序清单2-10，解决将float型值转换为int型值时可能会造成精度损失的问题。读取的输入值是一个字符串，比如“11.56”。你的程序应该应用indexOf和substring方法提取小数点前的美元数量，以及小数点后的美分数量。
import java.util.*;
public class test {
public static void main(String[] args) {
Scanner input = new Scanner(System.in);
// Receive the amount
System.out.print("Enter an amount in double, for example 11.56: ");
String amount = input.nextLine();
//精华两句
int remainingAmount = (int)(Integer.parseInt(amount.substring(0, amount.indexOf('.'))) * 100
+ Integer.parseInt(amount.substring(amount.indexOf('.')+1)));
// Find the number of one dollars
int numberOfOneDollars = remainingAmount / 100;
remainingAmount = remainingAmount % 100;
// Find the number of quarters in the remaining amount
int numberOfQuarters = remainingAmount / 25;
remainingAmount = remainingAmount % 25;
// Find the number of dimes in the remaining amount
int numberOfDimes = remainingAmount / 10;
remainingAmount = remainingAmount % 10;
// Find the number of nickels in the remaining amount
int numberOfNickels = remainingAmount / 5;
remainingAmount = remainingAmount % 5;
// Find the number of pennies in the remaining amount
int numberOfPennies = remainingAmount;
// Display results
System.out.println("Your amount " + amount + " consists of");
System.out.println(" " + numberOfOneDollars + " dollars");
System.out.println(" " + numberOfQuarters + " quarters ");
System.out.println(" " + numberOfDimes + " dimes");
System.out.println(" " + numberOfNickels + " nickels");
System.out.println(" " + numberOfPennies + " pennies");
input.close();
}
}
//Enter an amount in double, for example 11.56: 22.777
//Your amount 22.777 consists of
// 29 dollars
// 3 quarters
// 0 dimes
// 0 nickels
// 2 pennies
C5 循环
3种循环
例子：循环打印100次
1、while循环
初始化语句
while(循环继续条件) {
//循环体
语句（组）;
}
eg:
int count = 0
while(count < 100) {
System.out.printIn("Welcome to JAVA!");
count++;
}
2、do while
初始化语句
do(循环体){
//循环体
语句（组）;
} while(循环继续条件)
eg:
int count = 0
do {
System.out.printIn("Welcome to JAVA!");
count++;
} while(count < 100);
3、for循环
for(初始操作；循环继续条件；每次迭代后的操作){
//循环体
语句（组）;
}
eg:
for (int i = 0; i <100; i++){
System.out.printIn("Welcome to JAVA!");
}
打印99乘法表
嵌套循环
import java.util.*;
public class test {
public static void main(String[] args) {
System.out.println("Multiplication Table");
System.out.print(" ");
for (int j = 1; j <= 9; j++)
System.out.print(" " + j);
System.out.println("\n----------------------------------------");
for (int i = 1; i <= 9; i++) {
System.out.print(i + " |");
for (int j = 1; j <= 9; j++) {
System.out.printf("%4d", i * j);
}
System.out.println();
}
}
}
//Multiplication Table
// 1 2 3 4 5 6 7 8 9
//----------------------------------------
//1 | 1 2 3 4 5 6 7 8 9
//2 | 2 4 6 8 10 12 14 16 18
//3 | 3 6 9 12 15 18 21 24 27
//4 | 4 8 12 16 20 24 28 32 36
//5 | 5 10 15 20 25 30 35 40 45
//6 | 6 12 18 24 30 36 42 48 54
//7 | 7 14 21 28 35 42 49 56 63
//8 | 8 16 24 32 40 48 56 64 72
//9 | 9 18 27 36 45 54 63 72 81
5.14 示例学习-显示素数
要求：分5行显示前50个素数，每行包含10个数字
分解：
1、判断一个给定数是否是素数。
2、针对number = 1、2、3等测试
3、统计素数个数
4、打印每个素数，每行打印10个
算法：
设置打印出的素数个数常量NUMBER_OF_PRIMES;
使用count来对素数个数计数并初始值设置为0；
number初始值为2；
while(count <NUMBER_OF_PRIMES){
测试该数是否为素数；
if 该数是素数{
打印该素数并给count增加1；
}
给number 加1；
}
public class test {
public static void main(String[] args) {
final int NUMBER_OF_PRIMES = 50;
final int NUMBER_OF_PRIMES_PER_LINE = 10;
int count = 0;
int number = 2;
System.out.println("The first 50 prime numbers are \n");
//Repeatedly find prime numbers
while (count < NUMBER_OF_PRIMES) {
//Assume the number is prime
boolean isPrime = true; //Is the current number prime?
//Test whether number is prime
for(int divisor = 2; divisor <= number / 2; divisor++) {
if(number % divisor == 0) {//if true, number is not prime
isPrime = false;//Set isPrime to false
break;//Exit the for loop
}
}
//Display the prime number and increase the count
if(isPrime) {
count++;//Increase the count
if(count % NUMBER_OF_PRIMES_PER_LINE == 0){
//Display the number and advance to the neww line
System.out.println(number);
}
else
System.out.print(number + "");
}
//Check if the next number is prime
number++;
}
}
}
//The first 50 prime numbers are
//
//2357111317192329
//31374143475359616771
//7379838997101103107109113
//127131137139149151157163167173
//179181191193197199211223227229
5.19 打印金字塔型数字
编写一个嵌套的for循环，打印下面的输出：
1
1 2 1
1 2 4 2 1
1 2 4 8 4 2 1
1 2 4 8 16 8 4 2 1
1 2 4 8 16 32 16 8 4 2 1
1 2 4 8 16 32 64 32 16 8 4 2 1
1 2 4 8 16 32 64 128 64 32 16 8 4 2 1
public class test {
public static void main(String[] args) {
for(int line = 8;line >= 1;line--)
{
for(int i = 1;i <= 4 * (line-1);i++)
System.out.print(" ");
for(int i = 1;i <= (9 - line);i++)
System.out.printf("%4d",(int)Math.pow(2, i-1));
for(int i = (8 - line);i >= 1;i--)
System.out.printf("%4d",(int)Math.pow(2, i-1));
System.out.print("\n");
}
}
}
5.50 对大写字母计数
编写一个程序，提示用户输入一个字符串，然后显示该字符串大写字母的数目。
Enter a string: Welcome to Java
The number of uppercase letters is 2
import java.util.*;
public class test {
public static void main(String[] args) {
String userString;
int upperLetterCount = 0;
Scanner inputScanner = new Scanner(System.in);
System.out.print("Enter a string: ");
userString = inputScanner.nextLine();
for(int strIndex = 0;strIndex < userString.length();strIndex++)
if(userString.charAt(strIndex) >= 65 && userString.charAt(strIndex) <= 90)
upperLetterCount++;
System.out.printf("The number of uppercase letters is %d", upperLetterCount);
inputScanner.close();
}
}