3.1
1 import java.util.Scanner; 2 3 public class Main { 4 5 public static void main(String[] args) { 6 Scanner input = new Scanner (System.in); 7 8 System.out.print("Enter a, b, c: "); 9 double a = input.nextDouble(); 10 double b = input.nextDouble(); 11 double c = input.nextDouble(); 12 13 double pbs = b * b - 4 * a * c; 14 15 if (pbs < 0) 16 System.out.println("The equation has no real roots"); 17 else if (pbs == 0) 18 System.out.println("The equation has one root " + -b/(2*a)); 19 else 20 System.out.println("The equation has two roots " + (-b+Math.pow(pbs, 0.5))/(2*a) 21 + " and " + (-b-Math.pow(pbs, 0.5))/(2*a)); 22 } 23 }
3.3
1 import java.util.Scanner; 2 3 public class Main { 4 5 public static void main(String[] args) { 6 Scanner input = new Scanner (System.in); 7 8 System.out.print("Enter a, b, c, d, e, f: "); 9 double a = input.nextDouble(); 10 double b = input.nextDouble(); 11 double c = input.nextDouble(); 12 double d = input.nextDouble(); 13 double e = input.nextDouble(); 14 double f = input.nextDouble(); 15 16 double fm = a * d - b * c; 17 if(fm == 0) 18 System.out.println("The equation has no solution"); 19 else { 20 double x = (e*d - b*f) / fm; 21 double y = (a*f - e*c) / fm; 22 System.out.println("x is " + x + " and y is " + y); 23 } 24 } 25 }
3.4
1 package hello; 2 3 public class Main { 4 5 public static void main(String[] args) { 6 int m = (int)(Math.random() * 12 + 1); 7 String yue = "0"; 8 switch(m) { 9 case 1: yue = "January"; break; 10 case 2: yue = "February"; break; 11 case 3: yue = "March"; break; 12 case 4: yue = "April"; break; 13 case 5: yue = "May"; break; 14 case 6: yue = "June"; break; 15 case 7: yue = "July"; break; 16 case 8: yue = "Auguse"; break; 17 case 9: yue = "September"; break; 18 case 10: yue = "October"; break; 19 case 11: yue = "November"; break; 20 case 12: yue = "December"; break; 21 } 22 23 System.out.println(yue); 24 } 25 }
才开始忘记了break；造成每次都是输出December。