《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.");
    }
}