《Java语言程序设计与数据结构》编程练习答案（第三章）（一）

英文名：Introduction to Java Programming and Data Structures, Comprehensive Version, 11th Edition

3.1

import java.util.Scanner;public class book {
       public static void main(String[] args)    {
           Scanner input = new Scanner(System.in);        System.out.print("Enter a, b, c:");        double a = input.nextDouble();        double b = input.nextDouble();        double c = input.nextDouble();        double delta = b*b-4*a*c;        if(delta<0)            System.out.println("The equation has no real roots");        else if(delta==0)            System.out.println("The equation has one root "+(-1*b/2/a));        else        {
               double r1 = (-1*b+Math.pow(delta,0.5))/2/a;            double r2 = (-1*b-Math.pow(delta,0.5))/2/a;            System.out.println("The equation has two roots "+r1+" and "+r2);        }    }}

3.2

import java.util.Scanner;public class book {
       public static void main(String[] args)    {
           int number1 = (int)(System.currentTimeMillis()%10);        int number2 = (int)(System.currentTimeMillis()/10%10);        int number3 = (int)(System.currentTimeMillis()/100%10);        Scanner input = new Scanner(System.in);        System.out.print("What is "+number1+" + "+number2+" + "+number3+"? ");        int answer = input.nextInt();        System.out.println(number1+" + "+number2+" + "+number3+" = "+answer+" is "+(number1+number2+number3==answer));    }}

3.3

import java.util.Scanner;public class book {
       public static void main(String[] args)    {
           Scanner input = new Scanner(System.in);        System.out.print("Enter a, b, c, d, e, f:");        double a = input.nextDouble();        double b = input.nextDouble();        double c = input.nextDouble();        double d = input.nextDouble();        double e = input.nextDouble();        double f = input.nextDouble();        double jb = a*d-b*c;        if(jb==0)            System.out.println("The equation has no solution");        else            System.out.println("x is "+(e*d-b*f)/jb+" and y is "+(a*f-e*c)/jb);    }}

3.4

public class book {
       public static void main(String[] args)    {
           int month = (int)(Math.random()*12+1);        String[] names={
   "Feb","Jan","Mar","Apr","May","Jun","Jul","Aug","Sep","Oct","Nov","Dec"};        System.out.println("The number is "+month+", and the month is "+names[month-1]);    }}

3.5

import java.util.Scanner;public class book {
       public static void main(String[] args)    {
           Scanner input = new Scanner(System.in);        System.out.print("Enter today's day:");        int day = input.nextInt();        System.out.print("Enter the number of days elapsed since today:");        int plus = input.nextInt();        int result = (day+plus)%7;        String[] days = {
   "Sun","Mon","Tues","Wed","Thu","Fri","Sat"};        System.out.println("Today is "+days[day]+" and the future day is "+days[result]);    }}

3.6

import java.util.Scanner;public class book {
       public static void main(String[] args)    {
           Scanner input = new Scanner(System.in);        System.out.print("Enter weight in pounds:");        double pounds = input.nextDouble();        System.out.print("Enter feet:");        double feet = input.nextDouble();        System.out.print("Enter inches:");        double inches = input.nextDouble();        final double KILOS_PER_POUND = 0.45359237;        final double METERS_PER_INCH = 0.0254;        final double METERS_PER_FOOT = 0.3048;        double kilos = pounds*KILOS_PER_POUND;        double meters = feet*METERS_PER_FOOT+inches*METERS_PER_INCH;        double bmi = kilos/(meters*meters);        System.out.println("BMI is "+bmi);        if(bmi<18.5)            System.out.println("Underweight");        else if(bmi<25)            System.out.println("Normal");        else if(bmi<30)            System.out.println("Overweight");        else            System.out.println("Obese");    }}

3.7

import java.util.Scanner;public class book {
       public static void main(String[] args)    {
           Scanner input = new Scanner(System.in);        System.out.print("Enter an amount in double, for example 114.514:");        double amount = input.nextDouble();        int remainAmount = (int)(amount*100);        int numberOfDollars = remainAmount/100;        remainAmount%=100;        int numberOfQuarters = remainAmount/25;        remainAmount%=25;        int numberOfDimes = remainAmount/10;        remainAmount%=10;        int numberOfNickels = remainAmount/5;        remainAmount%=5;        int numberOfPennies = remainAmount;        System.out.println("Your amount "+amount+" consists of");        if(numberOfDollars>0)        {
               System.out.print(numberOfDollars);            if(numberOfDollars>1)                System.out.println(" dollars");            else                System.out.println(" dollar");        }        if(numberOfQuarters>0)        {
               System.out.print(numberOfQuarters);            if(numberOfQuarters>1)                System.out.println(" quarters");            else                System.out.println(" quarter");        }        if(numberOfDimes>0)        {
               System.out.print(numberOfDimes);            if(numberOfDimes>1)                System.out.println(" dimes");            else                System.out.println(" dime");        }        if(numberOfNickels>0)        {
               System.out.print(numberOfNickels);            if(numberOfNickels>1)                System.out.println(" nickels");            else                System.out.println(" nickel");        }        if(numberOfPennies>0)        {
               System.out.print(numberOfPennies);            if(numberOfPennies>1)                System.out.println(" pennies");            else                System.out.println(" penny");        }    }}

3.8

import java.util.Scanner;public class book {
       public static void main(String[] args)    {
           System.out.print("Input 3 integers:");        Scanner input = new Scanner(System.in);        int num1 = input.nextInt();        int num2 = input.nextInt();        int num3 = input.nextInt();        if(num1>num2)        {
               int tmp = num1;            num1 = num2;            num2 = tmp;        }        if(num2>num3)        {
               int tmp = num2;            num2 = num3;            num3 = tmp;        }        if(num1>num2)        {
               int tmp = num1;            num1 = num2;            num2 = tmp;        }        System.out.println(num1+" "+num2+" "+num3);    }}

3.9

import java.util.Scanner;public class book {
       public static void main(String[] args)    {
           int sum = 0;        Scanner input = new Scanner(System.in);        System.out.print("Enter the first 9 digits of an ISBN as integer: ");        int isbnNum = input.nextInt();        int old = isbnNum;        for(int i=9;i>=1;i--)        {
               sum+=isbnNum%10*i;            isbnNum/=10;        }        int tail = sum%11;        System.out.printf("The ISBN-10 number is %09d",old);        if(tail<10)            System.out.println(tail);        else            System.out.println("X");    }}

3.10

import java.util.Scanner;public class book {
       public static void main(String[] args)    {
           int number1 = (int)(Math.random()*100);        int number2 = (int)(Math.random()*100);        System.out.print("What is "+number1+" + "+number2+"? ");        Scanner input = new Scanner(System.in);        int answer = input.nextInt();        if(number1+number2==answer)            System.out.println("You are correct!");        else        {
               System.out.println("Your answer is wrong.");            System.out.println(number1+" + "+number2+" should be "+(number1+number2));        }    }}

3.11

import java.util.Scanner;public class book {
       public static void main(String[] args)    {
           Scanner input = new Scanner(System.in);        System.out.print("Enter the month number: ");        int month = input.nextInt();        System.out.print("Enter the year number: ");        int year = input.nextInt();        int[] months={
   31,28,31,30,31,30,31,31,30,31,30,31};        String[] monthNames={
   "Jan","Feb","Mar","Apr","May","Jun","Jul","Aug","Sep","Oct","Nov","Dec"};        boolean isLeapYear = (year%4==0&&year%100!=0)||(year%400==0);        if(isLeapYear)            months[1]=29;        System.out.println(monthNames[month-1]+" "+year+" has "+months[month-1]+" days.");    }}

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