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Thread: Switch

  1. #1
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    Default Switch

    Hey guys working on a simple switch program but not exactly a 100% if i can convert my what was a if statement into a switch or not. Any help would be awesome Thanks!

    import java.util.Scanner;
     
    public class math
    {
      public static void main(String[] args)
    {
     
     
    Scanner input = new Scanner(System.in);
     
    System.out.println(" Please select one of these options.");    
    System.out.println(" 1. Press A to add three numbers ");
    System.out.println(" 2. Press S to subtract two numbers ");
    System.out.println(" 3. Press M to multiply by three numbers ");
    System.out.println(" 4. Press D to divide by two numbers ");
    System.out.println(" 5. Press O to modulus two numbers ");
    System.out.println(" 6. Press E to quit the program ");
    System.out.println(" ");
     
    int option= input.nextInt();
     
     
        switch (option)
        {
        case 'A': {
          addition (); }
        break;
          case 'S': {
          subtract (); }
          break;
        case 'M': {
          multiply (); }
        break;
          case 'D': {
          divide (); }
          break;
          case 'O': {
          modulus (); }
          break;
          case 'E': {
          quit ();}
          break;
          default: 
     
          System.out.println("Not a option"); }
     
        }
     
     
        public static void addition(){
                 Scanner input = new Scanner( System.in );
                 float number1;
                 float number2;
                 float number3;
                 float sum;
     
          System.out.printf( "Enter first integer: " );
          number1 = input.nextInt();
          System.out.printf( "Enter second integer: " );
          number2 = input.nextInt();
          System.out.printf( "Enter Third integer: " );
          number3 = input.nextInt();
     
                 sum = number1 + number2 + number3;
                 System.out.printf( "Sum equals %f\n", sum);
        }
        public static void subtract(){
                 Scanner input = new Scanner( System.in );
                 float number1;
                 float number2;
                 float difference;
     
          System.out.printf( "Enter number to be subtracted: " );
          number1 = input.nextInt();
          System.out.printf( "Enter integer to subtract: " );
          number2 = input.nextInt();
     
     
                 difference = number1 - number2;
                 System.out.printf( "The difference is %f\n", difference);
     
        }
        public static void multiply(){
                Scanner input = new Scanner( System.in );
                 float number1;
                 float number2;
                 float number3;
                 float product;
     
          System.out.printf( "Enter first integer to multiply: " );
          number1 = input.nextInt();
          System.out.printf( "Enter second integer: " );
          number2 = input.nextInt();
          System.out.printf( "Enter Third integer: " );
          number3 = input.nextInt();
     
          product = number1 * number2 * number3;
          System.out.printf( "The product is %f\n", product);
     
        }
     
        public static void divide(){
              Scanner input = new Scanner( System.in );
               float number1;
               float number2;
               float dividen;
     
          System.out.printf( "Enter first integer: " );
          number1 = input.nextInt();
          System.out.printf( "Enter second integer: " );
          number2 = input.nextInt();
     
          dividen = number1 / number2;
          System.out.printf( "The dividen equals %f\n", dividen);
     
        }
     
        public static void modulus(){
             Scanner input = new Scanner ( System.in );
              float number1;
              float number2;
              float sum;
     
            System.out.printf( "Enter first integer: " );
            number1 = input.nextInt();
            System.out.printf( "Enter second ineger: " );
            number2 = input.nextInt();
     
            sum = number1 % number2;
            System.out.printf( "The answer equals %f\n", sum);
     
        }
     
        public static void quit(){
          System.out.printf( "Thank you for trying to use the program.");
          return; 
     
        }
     
      }
    Last edited by KillerToFu; March 21st, 2013 at 06:24 PM. Reason: changed quote to code tags


  2. #2
    Super Moderator Norm's Avatar
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    Default Re: Switch

    Can you explain what the problem is?

    The message printed for the default: should include the invalid option's value.
    If you don't understand my answer, don't ignore it, ask a question.

  3. #3
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    Default Re: Switch

    Sorry that's a good point didn't really specify what the problem was. The program reads the input but once it gets past that i can't get the program to start the lower operations. I'm using Dr.java this is the error
    java.util.InputMismatchException
    at java.util.Scanner.throwFor(Unknown Source)
    at java.util.Scanner.next(Unknown Source)
    at java.util.Scanner.nextInt(Unknown Source)
    at java.util.Scanner.nextInt(Unknown Source)
    at question4.main(question4.java:21)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Nativ e Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(Unknow n Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Un known Source)
    at java.lang.reflect.Method.invoke(Unknown Source)
    at edu.rice.cs.drjava.model.compiler.JavacCompiler.ru nCommand(JavacCompiler.java:272)

  4. #4
    Super Moderator Norm's Avatar
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    Default Re: Switch

    java.util.InputMismatchException
    at java.util.Scanner.throwFor(Unknown Source)
    at java.util.Scanner.next(Unknown Source)
    at java.util.Scanner.nextInt(Unknown Source)
    at java.util.Scanner.nextInt(Unknown Source)
    at question4.main(question4.java:21)
    The call to nextInt() at line 21 is trying to read an int value from the keyboard but the user is entering something that is not a numeric value. Use the next() or nextLine() method if you want to read a String not a number.
    If you don't understand my answer, don't ignore it, ask a question.

  5. The Following User Says Thank You to Norm For This Useful Post:

    KillerToFu (March 21st, 2013)

  6. #5
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    Default Re: Switch

    Thank you, this is kind of making me feel like i may not be able to go about it in this way. It makes my option not work in the string anymore. Says that i can not make option a variable, would i have to convert a Int to a String which i have read is not a simple solution, or is there another way?

  7. #6
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    Default Re: Switch

    To convert an int to a String just use Integer.parseInt(number); (Integer (Java Platform SE 7 ))

    Try to be consistent. Nearly all input from GUI's are strings first and then converted.

  8. The Following User Says Thank You to Starstreak For This Useful Post:

    KillerToFu (March 21st, 2013)

  9. #7
    Super Moderator Norm's Avatar
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    Default Re: Switch

    To convert an int to a String just use Integer.parseInt(number)
    Wrong. The parseInt() method converts a String to an int.
    Read the String class's API doc for methods to convert an int to a String.

    With Java 1.7 switch statements will work with Strings.
    If you don't understand my answer, don't ignore it, ask a question.

  10. #8
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    Default Re: Switch

    Thanks for locating my error. If you read the rest of my reply, you will see that I'm suggesting he start with a string, and then convert since Java GUIs take this approach.

  11. #9
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    Default Re: Switch

    Thanks a lot Norm really helped me figure that out. Was way easier then i was trying to make it, forgot to come back and thank you guys.


    This is what i ended up with.
    Scanner input = new Scanner( System.in );
    String aString = input.next();
    char choice = aString.charAt(0);


    switch (choice)
    {
    case 'A': {
    addition (); }

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