（3.2节+（3.8-3.16小节）+综合题）
3.2节
*3.1（代数：解一元二次方程）
import java.util.Scanner;
public class T1 {
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();
input.close();
double derta= Math.pow(b,2)-4*a*c ;//根的判别式
double r1= ( -b + Math.pow( Math.pow(b,2) - 4*a*c , 0.5 ) ) / 2*a ;
double r2=( -b - Math.pow( Math.pow(b,2) - 4*a*c , 0.5 ) ) / 2*a ;
if( derta>0 )
System.out.print("The equation has two roots:" + (float)r1 + " and " + (float)r2 );
else if ( derta==0 )
System.out.print("The equation has one root " + (float)r1);
else
System.out.print("The equation has no real roots");
}
}3.2（游戏：三个数的加法）
import java.util.Scanner;
public class T2 {
public static void main(String[] args) {
Scanner input=new Scanner(System.in);
int random1=(int) (Math.random()*10);
int random2=(int)(System.currentTimeMillis()%10);
int random3=(int)(System.currentTimeMillis()/7%10);
System.out.print(" 请输入这三个整数的和： ");
int number=input.nextInt();
input.close();
int sum=random1 + random2 + random3;
System.out.println(" 这三个随机数是 ："+ random1 + ", " + random2 + ", " + random3);
if(sum==number)
System.out.println("you are right!");
else
System.out.println("you are wrong!");
System.out.println("答案是："+ random1 + "+" + random2 + "+" + random3 + "=" + sum);
}
}
*3.3（代数：求解2x2线性方程）
import java.util.Scanner;
public class T3 {
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();
input.close();
double x=(e*d-b*f)/(a*d-b*c);
double y=(a*f-e*c)/(a*d-b*c);
if( (a*d-b*c)==0 )
System.out.println(" The equation has no solution ");
else
System.out.println(" x is " + x + " and y is " + y );
}
}
**3.4（随机月份）
public class T4 {
public static void main(String[] args) {
int random=(int) (Math.random()*12+1);
if (random==1)
System.out.println("random is " + random + " : January ");
else if (random==2)
System.out.println("random is " + random + " : February ");
else if (random==3)
System.out.println("random is " + random + " : March ");
else if (random==4)
System.out.println("random is " + random + " : April ");
else if (random==5)
System.out.println("random is " + random + " : May ");
else if (random==6)
System.out.println("random is " + random + " : June ");
else if (random==7)
System.out.println("random is " + random + " : July ");
else if (random==8)
System.out.println("random is " + random + " : August ");
else if (random==9)
System.out.println("random is " + random + " : September ");
else if (random==10)
System.out.println("random is " + random + " : October ");
else if (random==11)
System.out.println("random is " + random + " : November ");
else if (random==12)
System.out.println("random is " + random + " : December ");
}
}
*3.5（找到将来的日期）
import java.util.Scanner;
public class T5 {
public static void main(String[] args) {
Scanner input=new Scanner(System.in);
System.out.print("Enter today's day (0-6):");
int number=input.nextInt();
System.out.print("Enter the number of days elapsed since today:");
int days=input.nextInt();
input.close();
String day = null;
switch(number) {
case 0: day="Sunday";
break;
case 1: day="Monday";
break;
case 2: day="Tuesday";
break;
case 3: day="Wednesday";
break;
case 4: day="Thursday";
break;
case 5: day="Friday";
break;
case 6: day="Saturday";
break;
}
int afterDay=( number + (days%7) ) % 7 ;
String futureDay = null;
switch(afterDay) {
case 0: futureDay="Sunday";
break;
case 1: futureDay="Monday";
break;
case 2: futureDay="Tuesday";
break;
case 3: futureDay="Wednesday";
break;
case 4: futureDay="Thursday";
break;
case 5: futureDay="Friday";
break;
case 6: futureDay="Saturday";
break;
}
System.out.print("Today is " + day + " and the future day is " + futureDay );
}
}
*3.6（医疗应用程序：BMI）
import java.util.Scanner;
public class T6 {
public static void main(String[] args) {
//1英尺=0.3047999995367米
//1英寸=0.0254米
Scanner input=new Scanner(System.in);
System.out.print("Enter weight in pounds: ");
double weight=input.nextDouble();
System.out.print("Enter feet: ");
double feet=input.nextDouble();
System.out.print("Enter inches: ");
double inches=input.nextDouble();
input.close();
double weightInKilograms= weight*0.45359237 ;
double heightInMeters= inches*0.0254 + feet*0.3047999995367 ;
double bmi=weightInKilograms/(heightInMeters*heightInMeters);
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（财务应用程序：整钱兑零）
略，暂时不会，看见钱头就大o(╥﹏╥)o，不想去想，。。。。。。（用IF选择语句去做）
*3.8（对三个整数排序）
import java.util.Scanner;
public class T8 {
public static void main(String[] args) {
Scanner input=new Scanner(System.in);
System.out.print("请输入三个整数：");
int n1=input.nextInt();
int n2=input.nextInt();
int n3=input.nextInt();
input.close();
int temp;
if(n1>n2) {
temp=n1;
n1=n2;
n2=temp;
}//先交换1和2
if(n2>n3) {
temp=n2;
n2=n3;
n3=temp;
}//接着交换2和3
if(n1>n2) {
temp=n1;
n1=n2;
n2=temp;
}//接着交换1和3
System.out.print("从小到大排序为：" + n1 + " " + n2 + " "+ n3);
}
}
**3.9（商业：检查ISBN-10）
import java.util.Scanner;
public class T9 {
public static void main(String[] args) {
Scanner input=new Scanner(System.in);
System.out.print("Enter the first 9 digits of an ISBN as integer: ");
int d=input.nextInt();//输入9个数字
int d1=d/100000000%10;
int d2=d/10000000%10;
int d3=d/1000000%10;
int d4=d/100000%10;
int d5=d/10000%10;
int d6=d/1000%10;
int d7=d/100%10;
int d8=d/10%10;
int d9=d%10;
input.close();
int d10= (d1*1+d2*2+d3*3+d4*4+d5*5+d6*6+d7*7+d8*8+d9*9) % 11 ;
String dd="X";
if(d10==10)
System.out.print("The ISBN-10 number is " + d1+d2+d3+d4+d5+d6+d7+d8+d9+ dd );
else
System.out.print("The ISBN-10 number is " + d1+d2+d3+d4+d5+d6+d7+d8+d9+ d10 );
}
}
3.10（游戏：加法测验）
import java.util.Scanner;
public class T10 {
public static void main(String[] args) {
int number1=(int)(Math.random()*100);
int number2=(int)(Math.random()*100);
/* if(number1<number2) {
int temp=number1;
number1=number2;
number2=temp;
} */
System.out.print("What is " + number1 + " + " + number2 + " ? ");
Scanner input=new Scanner(System.in);
int answer=input.nextInt();
input.close();
if(number1 + number2 == answer)
System.out.println("You are right! ");
else {
System.out.println("Your answer is wrong.");
System.out.println( number1 + " + " + number2
+" should be " + (number1+number2) );
}
}
}
（3.8-3.16小节）
*3.11（给出一个月的总天数）
import java.util.Scanner;
public class T11 {
public static void main(String[] args) {
/* 一月大 二月平
三月大 四月小
五月大 六月小
七月大 八月大
九月小 十月大
十一月小 十二月大 */
System.out.print( " 请输入月份和年份： " );
Scanner input=new Scanner(System.in);
int month=input.nextInt();
int year=input.nextInt();
input.close();
String monthName=null;
String day=null;
//判定闰年，对2月份的影响
boolean isLeapYear=
( year%4==0 && year%10!=0 ) || ( year%400==0 );//判断是否是闰年
switch(month) {
case 1: monthName="January";
day="31";
break;
case 2: monthName="February";//特殊
if(isLeapYear)
day="29";
else
day="28";
break;
case 3: monthName="March";
day="31";
break;
case 4: monthName="April";
day="30";
break;
case 5: monthName="May";
day="31";
break;
case 6: monthName="June";
day="30";
break;
case 7: monthName="July";
day="31";
break;
case 8: monthName="August";
day="31";
break;
case 9: monthName="September";
day="30";
break;
case 10: monthName="October";
day="31";
break;
case 11: monthName="November";
day="30";
break;
case 12: monthName="December";
day="31";
break;
}
System.out.println( monthName +" "+ year + " has " + day + " days " );
}
}
3.12（回文数字）
import java.util.Scanner;
public class T12 {
public static void main(String[] args) {
Scanner input=new Scanner(System.in);
System.out.print("Enter a three-digit integer: ");
int d=input.nextInt();
input.close();
int d1=d%10;
int d2=d/10%10;
int d3=d/100%10;
if (d1==d3)
System.out.print( d + " is a palindrome");
else
System.out.print( d + " is not a palindrome");
}
}*3.13（财务应用程序：计算税款）
略
3.14（游戏：猜硬币的正反面）
import java.util.Scanner;
public class T14 {
public static void main(String[] args) {
// TODO Auto-generated method stub
System.out.print(" 请输入一个猜测值：");
Scanner input=new Scanner(System.in);
int answer=input.nextInt();
input.close();
int s=(int)(Math.random()*2);
String what=null;
switch(s) {
case 0: what=" 0 代表正面，1 代表反面. 随机数产生 0.";
break;
case 1: what=" 0 代表正面，1 代表反面. 随机数产生 1.";
break;
}
if(s==answer)
System.out.println( what + " You are right !");
else
System.out.println( what + " You are wrong.");
}
}
**3.15（游戏：彩票）
import java.util.Scanner;
public class T15 {
public static void main(String[] args) {
int lottery =(int)(Math.random()*1000);
Scanner input=new Scanner(System.in);
System.out.print("Enter your lottery pick (three digit): ");
int guess=input.nextInt();
input.close();
int l1=lottery%10;
int l2=lottery/10%10;
int l3=lottery/100%10;
int g1=guess%10;
int g2=guess/10%10;
int g3=guess/100%10;
System.out.println("The lottery number is: " + lottery );
if(guess==lottery)
System.out.println("Exact match: you win $10,000 ");
else if( (g1==l1 && g2==l3 && g3==l2 )
|| (g1==l2 && g2==l1 && g3==l3 )
|| (g1==l2 && g2==l3 && g3==l1 )
|| (g1==l3 && g2==l1 && g3==l2 )
|| (g1==l3 && g2==l2 && g3==l1 ) )
System.out.println("Match all digits: you win $3,000");
else if(l1==g1 || l1==g2 ||l1==g3
|| l2==g1 || l2==g2 || l2==g3
|| l3==g1 || l3==g2 || l3==g3 )
System.out.println("Match noe digit: you win $1,000");
else
System.out.println("Sorry, no match ");
}
}
3.16（随机点）
/*
* 我解释一下这一部分：(Math.random()*101 - Math.random()*1)
*
* 我是这样想的：
* 用double型的 Math.random()*101，来产生 [0,101) 区间里的整数和小数，
* 然后用 double型的 Math.random()*1，来产生 [0,1) 区间里的整数和小数，
* 用 [0,101) - [0,1) =[0,100]; //解释一下：[0,101)=[0,100]∪[100,101),
* 而[100,101)这一部分相当于[0,1)这一部分 ，他们的区间长度是一样的
*
* */ //当然用（int）类型产生随机数也可以，我这里想用double型的试试
public class T16 {
public static void main(String[] args) {
//X的上限是50，下限是-50；
// Y的上限是100，下限是-100.
double r1=((Math.random()*101 - Math.random()*1) - 50 );
double r2=((Math.random()*201 - Math.random()*1) - 100 );
System.out.println("产生的随机点是： （ " + r1 + " , " + r2 +" ) ");
}
}
*3.17（游戏：剪刀、石头、布）
import java.util.Scanner;
public class T17 {
public static void main(String[] args) {
Scanner input=new Scanner(System.in);
int random=(int) Math.random()*3;
System.out.print(" Scissor(0), Rock(1), Paper(2): ");
int number=input.nextInt();
input.close();
String word=null;
switch(random) {
case 0:word=" scissor. ";
break;
case 1:word=" rock. ";
break;
case 2:word=" paper. ";
break;
}
String word2=null;
if(random==0 && number==0)
word2=" You are scissor too. It is a draw ";
else if(random==0 && number==1)
word2=" You are rock. You won ";
else if(random==0 && number==2)
word2=" You are paper. You lose ";
else if(random==1 && number==0)
word2=" You are scissor. You lose ";
else if(random==1 && number==1)
word2=" You are rock too. It is a draw ";
else if(random==1 && number==2)
word2=" You are paper. You won ";
else if(random==2 && number==0)
word2=" You are scissor. You win ";
else if(random==2 && number==1)
word2=" You are rock. You lose ";
if(random==2 && number==2)
word2=" You are paper too. It is a draw ";
System.out.print("The computer is " + word + word2 );
}
}
*3.18（运输成本）
import java.util.Scanner;
public class T18 {
public static void main(String[] args) {
Scanner input=new Scanner(System.in);
System.out.print( " 请输入您的包裹重量： " );
double weight=input.nextDouble();
input.close();
if(weight>0 && weight<=1)
System.out.print( " 运输成本为 : " + 3.5*weight + " 美元 " );
if(weight>1 && weight<=3)
System.out.print( " 运输成本为 : " + 5.5*weight + " 美元 " );
if(weight>3 && weight<=10)
System.out.print( " 运输成本为 : " + 8.5*weight + " 美元 " );
if(weight>10 && weight<=20)
System.out.print( " 运输成本为 : " + 10.5*weight + " 美元 " );
else if(weight>20)
System.out.print( " the package cannot be shipped ");
}
}
**3.19（计算三角形的周长）
import java.util.Scanner;
public class T19 {
public static void main(String[] args) {
Scanner input=new Scanner(System.in);
System.out.print( " 请输入三角形的三条边 ： " );
int a=input.nextInt();
int b=input.nextInt();
int c=input.nextInt();
input.close();
if(a+b>c && a+c>b && b+c>a)
System.out.println("这个三角形的周长为： " + (a+b+c));
else
System.out.println(" 这些输入值不合法.");
}
}*20（科学：风寒温度）
import java.util.Scanner;
public class T20 {
public static void main(String[] args) {
Scanner input=new Scanner(System.in);
System.out.println("Enter the temperature in Fahrenheit between -58℃F and 41℃F：");
double temperature=input.nextDouble();
System.out.print("Enter the wind speed (>=2) in miles per hour:");
double windSpeed=input.nextDouble();
input.close();
double windChill= 35.74 + 0.6215*temperature - 35.75*Math.pow(windSpeed, 0.16)
+ 0.4275*temperature*Math.pow(windSpeed, 0.16);
if(temperature>=-58 && temperature<=41 && windSpeed>=2)
System.out.print("The wind chill index is " + windChill);
else if(temperature<-58 || temperature>41)
System.out.print(" 输入的温度不合法 ");
else if(windSpeed<2)
System.out.print(" 输入的风速不合法 ");
}
}
综合题
**3.21（科学：某天是星期几）
import java.util.Scanner;
public class T21 {
public static void main(String[] args) {
Scanner input=new Scanner(System.in);
System.out.print("Enter year: (e.g.,2012) : ");
int year=input.nextInt();
System.out.print("Enter month: 1-12: ");
int month=input.nextInt();
System.out.print("Enter the day of the month: 1-31: ");
int day=input.nextInt();
input.close();
int q ; //某月的第几天
q=day;
if(month==1) {
month=13;
year=year-1;
}
else if(month==2) {
month=14;
year=year-1;
}
int m ; /*是月份（注意：一月和二月分别记为上一年的13和14月，
其他月份照常，3为三月，4为四月，...，12为十二月 */
m=month;
int j = Math.abs( year/100 ); // 世纪数 |year/100|
int k=year%100;//该世纪的第几年
int h= ( q + (26*(m+1)/10) + k + (k/4) + (j/4) + (5*j) ) % 7 ;
String days = null;
switch(h) {
case 2: days="Monday";
break;
case 3: days="Tuesday";
break;
case 4: days="Wednesday";
break;
case 5: days="Thursday";
break;
case 6: days="Friday";
break;
case 0: days="Saturday";
break;
case 1: days="Sunday";
break;
}
System.out.print("Day of the week is " + days);
}
}
**3.22（几何：点是否在圆内？）
import java.util.Scanner;
public class T22 {
public static void main(String[] args) {
Scanner input=new Scanner(System.in);
System.out.print("Enter a point with two coordinates :");
float x=input.nextFloat();
float y=input.nextFloat();
input.close();
float d= (float) Math.pow( (Math.pow(x, 2) + Math.pow(y, 2)) , 0.5 );
String word=null;
if(d<=10)
word=" is";
else
word=" is not";
System.out.print("Point ("+ x +", "+ y +") " + word + " in the circle " );
}
}
**3.23（几何：点是否在矩形内？）
import java.util.Scanner;
public class T23 {
public static void main(String[] args) {
Scanner input=new Scanner(System.in);
System.out.print("Enter a point with two coordinates :");
float x=input.nextFloat();
float y=input.nextFloat();
input.close();
String word=null;
if( (x-0)<=10/2 && (y-0)<=5/2 )
word=" is";
else
word=" is not";
System.out.print("Point ("+ x +", "+ y +") " + word + " in the rectangle " );
}
}
**3.24（游戏：挑一张牌）
public class T24 {
public static void main(String[] args) {
int random=(int)(Math.random()*13);
int random1=(int)(Math.random()*4) ;
String word=null;
switch(random) {
case 0: word=" Ace ";
break;
case 1: word=" 2 ";
break;
case 2: word=" 3 ";
break;
case 3: word=" 4 ";
break;
case 4: word=" 5 ";
break;
case 5: word=" 6 ";
break;
case 6: word=" 7 ";
break;
case 7: word=" 8 ";
break;
case 8: word=" 9 ";
break;
case 9: word=" 10 ";
break;
case 10: word=" Jack ";
break;
case 11: word=" Queen ";
break;
case 12: word=" King ";
break;
}
String word1=null;
switch(random1) {
case 0: word1=" Clubs ";
break;
case 1: word1=" Diamonds ";
break;
case 2: word1=" Hearts ";
break;
case 3: word1=" Spades ";
break;
}
System.out.print("The card you picked is " + word + " of " + word1);
}
}
*3.25（几何：交点）
import java.util.Scanner;
public class T25 {
public static void main(String[] args) {
Scanner input=new Scanner(System.in);
System.out.print("Enter x1, y1, x2, y2, x3, y3, x4, y4: ");
float x1=input.nextFloat();
float y1=input.nextFloat();
float x2=input.nextFloat();
float y2=input.nextFloat();
float x3=input.nextFloat();
float y3=input.nextFloat();
float x4=input.nextFloat();
float y4=input.nextFloat();
input.close();
float x=( ((y1-y2)*x1-(x1-x2)*y1)*(-(x3-x4)) - (-(x1-x2))*((y3-y4)*x3-(x3-x4)*y3) )
/ ( (y1-y2)*(-(x3-x4)) - (-(x1-x2))*(y3-y4) );
float y=( (y1-y2)*((y3-y4)*x3-(x3-x4)*y3) - ((y1-y2)*x1-(x1-x2)*y1)*(y3-y4) )
/ ( (y1-y2)*(-(x3-x4)) - (-(x1-x2))*(y3-y4) );
float t=( (y1-y2)*(-(x3-x4)) - (-(x1-x2))*(y3-y4) ) ;
if(t==0)
System.out.print(" The two lines are parallel ");
else
System.out.print("The intersecting point is at (" + x + ", " + y + ")");
}
}
3.26（使用操作符&&、|| 和 ^）
import java.util.Scanner;
public class T26 {
public static void main(String[] args) {
Scanner input=new Scanner(System.in);
System.out.print("Enter an integer: ");
int integer=input.nextInt();
input.close();
boolean answer=(integer%5==0 && integer%6==0);
boolean answer1=(integer%5==0 || integer%6==0);
boolean answer2=(integer%5==0 ^ integer%6==0);
System.out.println(" Is " + integer + " divisible by 5 and 6 ? " + answer );
System.out.println(" Is " + integer + " divisible by 5 or 6 ? " + answer1 );
System.out.println(" Is " + integer + " divisible by 5 or 6, but not both ? " + answer2 );
}
}
**3.27（几何：点是否在三角形内？）
我是看某大神的博客得到的启发：（里面还有很多不同的证明方法）
https://blog.csdn.net/dageda1991/article/details/77875637
在本书 第四章 的第103页，P103 有求角度的详细说明。
提示：内角和等于360°
1.这种方法最好理解，即对于△ABC内的某一点P，连接PA、PB、PC得到三条线段，当且仅当三条线段组成的三个夹角和为360°的时候，该点才位于三角形内部。
2.类似的还有，P与ABC三个顶点组成的三个三角形，面积之和等于△ABC的面积，同样可以证明点P位于三角形内部。
import java.util.Scanner;
public class T27 {
public static void main(String[] args) {
Scanner input=new Scanner(System.in);
System.out.print("Enter a point's x- and y-coordinates: ");
float x=input.nextFloat();
float y=input.nextFloat();
input.close();
int x1=0, y1=0; //点 O(x1,y1)
int x2=200, y2=0; //点 B(x2,y2)
int x3=0, y3=100; //点 A(x3,y3)
// 设点 P 为(x,y).
//先计算第一个 角∠APO=one ，必须先知道边AO,OP,AP
double LAO=100;
double LOP=Math.sqrt((x-x1)*(x-x1) + (y-y1)*(y-y1));
double LAP=Math.sqrt((x3-x)*(x3-x) + (y3-y)*(y3-y));
double one=Math.toDegrees( Math.acos((LAO*LAO - LOP*LOP - LAP*LAP) / (-2*LOP*LAP) ) ) ;
//计算第二个 角∠APB=two ,必须先知道它的三条边AB,PB,AP
double LAB=Math.sqrt( (x2-x3)*(x2-x3) + (y2-y3)*(y2-y3) );
//double LAP=Math.sqrt((x3-x)*(x3-x) + (y3-y)*(y3-y));
double LPB=Math.sqrt((x2-x)*(x2-x) + (y2-y)*(y2-y));
double two=Math.toDegrees( Math.acos((LAB*LAB - LAP*LAP - LPB*LPB) / (-2*LAP*LPB) ) ) ;
//计算第三个 角∠OPB=three ，必须知道它的三条边OB,PB,OP
double LOB=200;
//double LPB=Math.sqrt((x2-x)*(x2-x) + (y2-y)*(y2-y));
//double LOP=Math.sqrt((x-x1)*(x-x1) + (y-y1)*(y-y1));
double three=Math.toDegrees( Math.acos((LOB*LOB - LOP*LOP - LPB*LPB) / (-2*LOP*LPB) ) ) ;
//如果三个角相加为 360° ，则这个点在三角形内部
String word=null;
if(one+two+three==360)
word=" is ";
else
word=" is not ";
System.out.print("The point " + word + " in the triangle ");
}
}
**3.28（几何：两个矩形）
import java.util.Scanner;
public class T28 {
public static void main(String[] args) {
Scanner input =new Scanner(System.in);
System.out.print("Enter r1's center x-, y-coordinates, width, and height: ");
float x1=input.nextFloat() ;
float y1=input.nextFloat() ;
float w1=input.nextFloat() ;
float h1=input.nextFloat() ;
System.out.print("Enter r2's center x-, y-coordinates, width, and height: ");
float x2=input.nextFloat() ;
float y2=input.nextFloat() ;
float w2=input.nextFloat() ;
float h2=input.nextFloat() ;
input.close();
if( (x1-w1/2<=x2-w2/2) && (x2+w2/2<=x1+w1/2)
&&(y2+h2/2<=y1+h1/2) && (y2-h2/2>=y1-h1/2))
System.out.print(" r2 is inside r1 ");
else if ( ((y2+h2/2>y1-h1/2) && (x2-w2/2<x1+w1/2))
|| ((y2-h2/2<y1+h1/2) && (x2+w2/2>x1-w1/2) ) )
System.out.print(" r2 overlaps r1 ");
else
System.out.print(" r2 dose not overlap r1 ");
}
}
**3.29（几何：两个圆）
import java.util.Scanner;
public class T29 {
public static void main(String[] args) {
Scanner input=new Scanner(System.in);
System.out.print( "Enter circle1's center x-, y-coordinates, and radius: ");
float x1=input.nextFloat();
float y1=input.nextFloat();
float r1=input.nextFloat();
System.out.print( "Enter circle2's center x-, y-coordinates, and radius: ");
float x2=input.nextFloat();
float y2=input.nextFloat();
float r2=input.nextFloat();
input.close();
float d=(float) Math.sqrt( (x1-x2)*(x1-x2) + (y1-y2)*(y1-y2) );
if( d <= Math.abs(r1-r2) )
System.out.print(" cricle2 is inside circle1 ");
else if( d <= (r1+r2) )
System.out.print(" cricle2 overlaps circle1 ");
else
System.out.print(" cricle2 does not overlap circle1 ");
}
}
*3.30（当前时间）
略（不会）
一看见数时间数钱的我就烦┭┮﹏┭┮
*3.31（金融：货币兑换）
import java.util.Scanner;
public class T31 {
public static void main(String[] args) {
Scanner input = new Scanner(System.in);
System.out.print("Enter the exchange rate from dollars to RMB: ");
float exchangeRate=input.nextFloat();
System.out.print("Enter 0 to convert dollars to RMB and 1 vice versa: ");
int number=input.nextInt();
if (number==0) {
System.out.print("Enter the dollar amount:");
float dollars=input.nextFloat();
System.out.print(" $"+dollars+" is " +(exchangeRate*dollars)+" yuan");
}
else if(number==1) {
System.out.print("Enter the RMB amount:");
float emb=input.nextFloat();
System.out.print( emb + " yuan is $" + (emb/exchangeRate));
}
else
System.out.print(" Incorrect input ");
input.close();
}
}*3.32（几何：点的位置）
import java.util.Scanner;
public class T32 {
public static void main(String[] args) {
Scanner input = new Scanner(System.in);
System.out.print("Enter three points for p0, p1, p2:");
float x0=input.nextFloat();
float y0=input.nextFloat();
float x1=input.nextFloat();
float y1=input.nextFloat();
float x2=input.nextFloat();
float y2=input.nextFloat();
input.close();
float number= (x1-x0)*(y2-y0) - (x2-x0)*(y1-y0) ;
if(number>0)
System.out.print(" ("+x2+", "+y2+") is on the left side of "
+ "the line from ("+x0+", "+y0+") to ("+x1+", "+y1+") ");
else if(number==0)
System.out.print(" ("+x2+", "+y2+") is on the the line "
+ "from ("+x0+", "+y0+") to ("+x1+", "+y1+") ");
else if(number<0)
System.out.print(" ("+x2+", "+y2+") is on the right side of "
+ "the line from ("+x0+", "+y0+") to ("+x1+", "+y1+") ");
}
}
*3.33（金融：比较成本）
import java.util.Scanner;
public class T33 {
public static void main(String[] args) {
Scanner input = new Scanner(System.in);
System.out.print("Enter weight and price for package 1:");
float weight1=input.nextFloat();
float price1=input.nextFloat();
System.out.print("Enter weight and price for package 2:");
float weight2=input.nextFloat();
float price2=input.nextFloat();
input.close();
if((weight1/price1) > (weight2/price2))
System.out.print("Package 1 has a better price");
else if((weight1/price1) < (weight2/price2))
System.out.print("Package 2 has a better price");
else if((weight1/price1) == (weight2/price2))
System.out.print("Two packages have the same price");
}
}
*3.34（几何：线段上的点）
这一题一定要理解清楚，这题和 *3.32的题目有什么不同。
*3.32的题目是测试一个点是否在一个无限长的直线上，而这题是测试一个点是否在一个线段上，这里最容易混淆。
线段上：则看 点p2到点p1的距离 + 点p2到点p0的距离 是否等于线段p0p1的线段长度，就OK了。
import java.util.Scanner;
public class T34 {
public static void main(String[] args) {
Scanner input = new Scanner(System.in);
System.out.print("Enter three points for p0, p1, p2:");
float x0=input.nextFloat();
float y0=input.nextFloat();
float x1=input.nextFloat();
float y1=input.nextFloat();
float x2=input.nextFloat();
float y2=input.nextFloat();
input.close();
float lp0p1=(float) Math.sqrt((x1-x0)*(x1-x0) + (y1-y0)*(y1-y0));
float lp0p2=(float) Math.sqrt((x2-x0)*(x2-x0) + (y2-y0)*(y2-y0));
float lp1p2=(float) Math.sqrt((x2-x1)*(x2-x1) + (y2-y1)*(y2-y1));
if(lp0p1==lp0p2+lp1p2)
System.out.print(" ("+x2+", "+y2+") is on the line "
+ "segment from ("+x0+", "+y0+") to ("+x1+", "+y1+") ");
else
System.out.print(" ("+x2+", "+y2+") is not on the line "
+ "segment from ("+x0+", "+y0+") to ("+x1+", "+y1+") ");
}
}
