Java-菜单循环和数学计算

Question

I'm working on a program that will give the user a menu, allow them to select an option, then ask for different numbers to do a calculation based on their menu choice. I've started with the basic outline of the program, but I need help getting loops implemented and working.

Here is my code so far:

import java.util.Scanner;

public class LB04Alexander {

public static void main(String[] args) {
    Scanner input = new Scanner(System.in);
    System.out.println("This program will perform several types of calculations.");
    System.out.println();
    System.out.println("-MENU-");
    System.out.println("Select from the following menu options:");
    System.out.println("1 - Compute integer powers of a number");
    System.out.println("2 - Compute a factorial");
    System.out.println("3 - Compute a square root");
    System.out.println("4 - Compute a cube root");
    System.out.println("5 - Compute an exponential");
    System.out.println("6 - Compute the sine of an angle");
    System.out.println("7 - Compute the cosine of an angle");
    System.out.println("8 - Convert a positive integer to binary");
    System.out.println("9 - Exit");
    System.out.println("Please enter the number corresponding to your choice:");

    int menuChoice = input.nextInt();
    while (menuChoice >= 1 && menuChoice <= 9); {
        switch (menuChoice) {
        case 1:
            System.out.println("You have chosen to compute integer powers of a number.");
            System.out.println("Please enter any number for the base:");
            double base1 = input.nextDouble();
            System.out.println("Now, enter a non-negative integer for the exponent:");
            int exponent1 = input.nextInt();
            if (exponent1 < 0)
                System.out.println("Error: exponent is negitive.");
            else
                System.out.println(base1 + "^" + exponent1 + " = " + "");
            break;
        case 2:
            System.out.println("You have chosen to compute a factorial (n!) of a non-negative integer.");
            System.out.println("Please enter a non-negitive integer for n:");
            long fact = input.nextLong();
            int result = 1; 
            if (fact < 0) 
                System.out.println("Error: integer is negitive.");
            else if (fact >= 127)
                System.out.println("Error: Answer too large to calculate");
            else
                for (int i = 1; i <= fact; i++) {
                    result = result * i;
                }
            System.out.println(fact + "! = " + result );
            break;
        case 3:
            System.out.println("You have chosen to compute a square root.");
            break;
        case 4:
            System.out.println("You have chosen to compute a cube root.");
            break;
        case 5:
            System.out.println("You have chosen to compute an exponential.");   
            break;
        case 6:
            System.out.println("You have chosen to compute the sine of an angle."); 
            break;
        case 7:
            System.out.println("You have chosen to compute the cosine of an angle.");   
            break;
        case 8:
            System.out.println("You have chosen to convert a positive integer to binary");  
            break;
        case 9:
            System.out.println("You have chosen to exit");
            System.out.println("Program LB04Alexander is now terminating...");
            input.close();
            System.out.println("The program has ended. Goodbye.");
            break;
        default:
            System.out.println("Invalid menu choice, please try again.");
            break;

        } }


}
}

The first problem I'm having is getting the menu to loop the right way. it either doesn't work, or loops forever.

Answer 1

while (menuChoice >= 1 && menuChoice <= 9);

Get rid of that semi-colon. When your choice satisfies the condition, it loops forever. When it doesn't, it will quit immediately (since none of the cases match) after printing out Invalid menu choice, please try again. .

Answer 2

Try this, it is somewhat more modular than yours but about the same ...

    import java.util.Scanner;

    public class LB04Alexander {

      public static final Scanner SCANNER = new Scanner(System.in);

      public static void main(String[] args) {
        int choice;

        showMenu();
        while((choice = getInt("Please enter the number corresponding to your choice:")) != 9) {
          doCalculation(choice);
          showMenu();
        }
      }

      public static void showMenu() {
        System.out.println("This program will preform several types on calculations.");
        System.out.println();
        System.out.println("===============MENU=====================");
        System.out.println("Select from the following menu options:");
        System.out.println("1 - Compute integer powers of a number");
        System.out.println("2 - Compute a factorial");
        System.out.println("3 - Compute a square root");
        System.out.println("4 - Compute a cube root");
        System.out.println("5 - Compute an exponential");
        System.out.println("6 - Compute the sine of an angle");
        System.out.println("7 - Compute the cosine of an angle");
        System.out.println("8 - Convert a positive integer to binary");
        System.out.println("9 - Exit");
        System.out.println("========================================");

      }


      private static void doCalculation(int choice) {
        switch (choice) {
        case 1:
          System.out.println("\nYou have chosen to compute integer powers of a number.");
          double base1 = getDouble("Please enter the number corresponding to your choice:");
          int exponent1 = getInt("Now, enter a non-negative integer for the exponent:");
          System.out.println(base1 + "^" + exponent1 + " = " + "");
          break;
        case 2:
          System.out.println("You have chosen to compute a factorial (n!) of a non-negative integer.");
          long fact = getLong("Please enter a non-negitive integer for n:");
          int result = 1;
          if (fact < 0)
            System.out.println("Error: integer is negitive.");
          else if (fact >= 127)
            System.out.println("Error: Answer too large to calculate");
          else
            for (int i = 1; i <= fact; i++) {
              result = result * i;
            }
          System.out.println(fact + "! = " + result );
          break;
        case 3:
          System.out.println("You have chosen to compute a square root.");
          break;
        case 4:
          System.out.println("You have chosen to compute a cube root.");
          break;
        case 5:
          System.out.println("You have chosen to compute an exponential.");
          break;
        case 6:
          System.out.println("You have chosen to compute the sine of an angle.");
          break;
        case 7:
          System.out.println("You have chosen to compute the cosine of an angle.");
          break;
        case 8:
          System.out.println("You have chosen to convert a positive integer to binary");
          break;
        default:
          System.out.println("Invalid menu choice, please try again.");
          break;
        }
      }

      private static int getInt(String prompt) {
        boolean unassigned = true;
        int value = 0;
        while(unassigned) {
          try {
              System.out.println(prompt);
              value = SCANNER.nextInt();
              unassigned = false;
          }
          catch (IllegalArgumentException e) {}
        }
          System.out.println("[" + value + "]");

        return value;
      }

      private static double getDouble(String prompt) {
        boolean unassigned = true;
        double value = 0;
        while(unassigned) {
          try {
              System.out.println(prompt);
              value = SCANNER.nextDouble();
              unassigned = false;
          }
          catch (IllegalArgumentException e) {}
        }
          System.out.println("[" + value + "]");
        return value;
      }

      private static long getLong(String prompt) {
        boolean unassigned = true;
        long value = 0;
        while(unassigned) {
          try {
              System.out.println(prompt);
              value = SCANNER.nextLong();
              unassigned = false;
          }
          catch (IllegalArgumentException e) {}
        }
          System.out.println("[" + value + "]");

        return value;
      }
    }