java语言基础练习3

 1 package 编程练习题chapter3;  2 import java.util.Scanner;  3 public class Exercise3_1 {  4 public static void main(String[] args){  5 Scanner input = new Scanner(System.in);  6 System.out.print("Enter a, b, c: ");  7 double a = input.nextDouble();  8 double b = input.nextDouble();  9 double c = input.nextDouble(); 10 11 double discriminant = b * b - 4 * a *c; 12 13 if (discriminant < 0){ 14 System.out.println("The equation has no roots"); 15  } 16 else if (discriminant == 0){ 17 double r1 = -b / (2 * a); 18 System.out.println("The root is " + r1); 19  } 20 else { 21 double r1 = (-b + Math.pow(discriminant, 0.5)) / (2 * a); 22 double r2 = (-b - Math.pow(discriminant, 0.5)) / (2 * a); 23 System.out.println("The roots is " + r1 + " and " + r2); 24  } 25  } 26 }

 1 package 编程练习题chapter3;  2 import java.util.Scanner;  3 public class Exercise3_2 {  4 public static void main(String[] args){  5 Scanner input = new Scanner(System.in);  6  7 System.out.print("Enter an integer: ");  8 int number = input.nextInt();  9 10 System.out.println("Is " + number + " an even number? " + (number % 2 == 0)); 11  } 12 }

 1 package 编程练习题chapter3;  2 import java.util.Scanner;  3 public class Exercise3_3 {  4 public static void main (String[] args){  5 Scanner input = new Scanner(System.in);  6 System.out.print("Enter a, b, c, d, e, f: ");  7  8 double a = input.nextDouble();  9 double b = input.nextDouble(); 10 double c = input.nextDouble(); 11 double d = input.nextDouble(); 12 double e = input.nextDouble(); 13 double f = input.nextDouble(); 14 double detA = a * d - b * c; 15 16 if (detA == 0){ 17 System.out.println("The equationhas no solution"); 18  } 19 else { 20 double x = (e * d - b * f) / detA; 21 double y = (a * f - e * c) / detA; 22 System.out.println("x is " + x + " and y is " + y); 23  } 24  } 25 }

 1 package 编程练习题chapter3;  2 import javax.swing.*;  3 public class Exercise3_4 {  4 public static void main(String[] args){  5 int number1 = (int)(System.currentTimeMillis() % 100);  6 int number2 = (int)(System.currentTimeMillis() * 7 % 100);  7  8 String resultString = JOptionPane.showInputDialog("What is " + number1 + " + " + number2 + "?");  9 10 int result = Integer.parseInt(resultString); 11 12 JOptionPane.showConfirmDialog( java语言基础练习3null, number1 + " + " + number2 + "=" + result + " is " + (number1 + number2 == result)); 13 14  } 15 }

 1 package 编程练习题chapter3;  2 import java.util.*;  3 public class Exercise3_5 {  4 public static void main (String[] args){  5 Scanner input = new Scanner(System.in);  6 int number1 = (int)(System.currentTimeMillis() % 10);  7 int number2 = (int)(System.currentTimeMillis() * 7 % 10);  8 int number3 = (int)(System.currentTimeMillis() * 3 % 10);  9 10 System.out.print("What is " + number1 + " + " + number2 + " + " + number3 + "?"); 11 12 int answer = input.nextInt(); 13 14 System.out.println(number1 + " + " + number2 + " + " + number3 + " = " + answer + " is " + 15 (number1 + number2 + number3 == answer)); 16  } 17 }

 1 package 编程练习题chapter3;  2 import java.util.*;  3 public class Exercise3_6 {  4 public static void main(String[] args) {  5 Scanner input = new Scanner(System.in);  6  7 System.out.print("Enter weight in pounds: ");  8 double weight = input.nextDouble();  9 10 System.out.print("Enter feet: "); 11 double feet = input.nextDouble(); 12 13 System.out.print("Enter inches: "); 14 double inches = input.nextDouble(); 15 16 double height = feet * 12 + inches; 17 double bmi = weight * 0. / ((height * 0.0254) * (height * 0.0254)); 18 System.out.println("Your BMI is " + bmi); 19 20 if (bmi < 16) 21 System.out.println("You are seriously underweight"); 22 else if (bmi < 18) 23 System.out.println("You are underweight"); 24 else if (bmi < 24) 25 System.out.println("You are normal weight"); 26 else if (bmi < 29) 27 System.out.println("You are over weight"); 28 else if (bmi < 35) 29 System.out.println("You are seriously over weight"); 30 else 31 System.out.println("You are gravely over weight"); 32  } 33 }

 1 package 编程练习题chapter3;  2  3 public class Exercise3_8 {  4 public static void main(String[] args){  5 java.util.Scanner input = new java.util.Scanner(System.in);  6 System.out.print("Enetr three integer: ");  7 int num1 = input.nextInt();  8 int num2 = input.nextInt();  9 int num3 = input.nextInt(); 10 11 if (num1 > num2) { 12 int temp = num1; 13 num1 = num2; 14 num2 = temp; 15  } 16 17 if (num2 > num3) { 18 int temp = num2; 19 num2 = num3; 20 num3 = temp; 21  } 22 23 if (num1 > num2) { 24 int temp = num1; 25 num1 = num2; 26 num2 = temp; 27  } 28 System.out.println("The sorted numbers are " + num1 + " " + num2 + " " + num3); 29  } 30 31 }

 1 package 编程练习题chapter3;  2  3 public class Exercise3_11 {  4 public static void main(String[] args){  5 java.util.Scanner input = new java.util.Scanner(System.in);  6  7 System.out.print("Enter a month in the year: ");  8 int month = input.nextInt();  9 10 System.out.print("Enetr a year: "); 11 int year = input.nextInt(); 12 13 int numberOfDaysInMonth = 0; 14 15 switch(month){ 16 case 1: 17 System.out.print("January " + year); 18 numberOfDaysInMonth = 31; 19 break; 20 case 2: 21 System.out.print("February " + year); 22 if (year % 400 == 0 || (year % 4 == 0 && year % 100 != 0)){ 23 numberOfDaysInMonth = 29; 24  } 25 else { 26 numberOfDaysInMonth = 28; 27  } 28 break; 29 case 3: 30 System.out.print("March " + year); 31 numberOfDaysInMonth = 31; 32 break; 33 case 4: 34 System.out.print("April " + year); 35 numberOfDaysInMonth = 30; 36 break; 37 case 5: 38 System.out.print("May " + year); 39 numberOfDaysInMonth = 31; 40 break; 41 case 6: 42 System.out.print("June " + year); 43 numberOfDaysInMonth = 30; 44 break; 45 case 7: 46 System.out.print("July " + year); 47 numberOfDaysInMonth = 31; 48 break; 49 case 8: 50 System.out.print("August " + year); 51 numberOfDaysInMonth = 31; 52 break; 53 case 9: 54 System.out.print("September " + year); 55 numberOfDaysInMonth = 30; 56 break; 57 case 10: 58 System.out.print("October " + year); 59 numberOfDaysInMonth = 31; 60 break; 61 case 11: 62 System.out.print("November " + year); 63 numberOfDaysInMonth = 30; 64 break; 65 case 12: 66 System.out.print("December " + year); 67 numberOfDaysInMonth = 31; 68 break; 69  } 70 System.out.println(" has " + numberOfDaysInMonth + " days"); 71  } 72 73 }