Thread: Assignment Problem. Please help

Hi

I need to make a program. Part of it requires the user to enter A B and C and display it. I am trying to make the program accept only A B and C and loop back if another string is entered.

   System.out.println("Please Choose One of the following letters: A, B or C: ");//Asks the User for his input
        Scanner sc = new Scanner(System.in); //Accepts the Users input
        String Selection = sc.nextLine();
 
     if (!Selection.equals("A")){
        do {
 
                System.out.println("*Please Choose One of the following letters: A, B or C: ");//Asks the User for his input
                Selection = sc.nextLine();
 
        }
        while (!Selection.equals("A"));
     }   
 
       }
 
    }

This "works"

BUT

When I do   if (!Selection.equals("A") || !Selection.equals("B") || !Selection.equals("C") )

and

while  (!Selection.equals("A") || !Selection.equals("B") || !Selection.equals("C") )

the program doesnt work as intended...


Any idea's please?

I need either A, B or C to be true though. Not all three? :/

....but then it doesn't work well...I cannot understand why. I spent 2 hours playing around with it.

if its true... it still outputs the statement

 
System.out.println("*Please Choose One of the following letters: A, B or C: ");

which is the code inside the condition....

ok, I'll try make myself more clear.

   System.out.println("Please Choose One of the following letters: A, B or C: ");//Asks the User for his input
        Scanner sc = new Scanner(System.in); //Accepts the Users input
        String Selection = sc.nextLine();
 
     if (!Selection.equals("A")){
        do {
 
                System.out.println("INVALID ----- Please Choose One of the following letters: A, B or C: ");//Asks the User for his input
                Selection = sc.nextLine();
 
        }
        while (!Selection.equals("A"));
     }   
 
       }
 
    }

This piece of code works. BUT the problem is that I want the program to run the conditional statement only if A B or C are not entered.
At the moment, the statement only runs if the statement is NOT A.

When I edit the statement to become

 
 if (!Selection.equals("A") || !Selection.equals("B") || !Selection.equals("C")){
        do {
 
                System.out.println("INVALID ----- Please Choose One of the following letters: A, B or C: ");//Asks the User for his input
                Selection = sc.nextLine();
 
        }
        while (!Selection.equals("A") || !Selection.equals("B") || !Selection.equals("C"));
     }

The Statement still runs even if I enter A B or C. I cannot understand why the or statement is having this effect on the program.

Hope this better explains my situation

ahhhhhhhhhhhh....okokok.. can't believe i diidnt see that... I think I got it....

Thanks.. I'll try it out...

Is it possible to shorten the if statement?

if (!Selection.equals("A") & !Selection.equals("B") & !Selection.equals("C")){

I need something like

!Selection.equals("A" & "B" & "C");

But it doesnt let me do that. I get a bad operand error

See Learning the Java Language > Language Basics > Operators

& is bitwise AND
&& is logical AND.

You want logical AND.

Originally Posted by melki0795

Is it possible to shorten the if statement?

You could use regular expressions but adding complexity to shorten code is a poor trade.

What do you mean by regular expressions? May you give me an example? ANy ideas of how I can make this program better so?

Regular expressions allow you to test if a string matches a certain pattern. They have their place but try and avoid them if there is an alternative. In your case a couple of if .equals() is more appropriate.

Originally Posted by melki0795

ANy ideas of how I can make this program better so?

Pen and paper. Write down exactly what you want the program to do, step by step. It's called pseudocode and it's very helpful in wrapping your head around the logic and flow of a program.

Thanks m8...

Have you read your methodswitch() method? There aren't a lot of options.

import java.util.Scanner;
public class Interrogator3
{
    public static void main(String[] args) {
 
 
 
        //Welcoming Message
        System.out.println("Welcome to the program! ");
        System.out.println("");
 
        //The user will be asked to enter his letter of choice.
        System.out.println("Please Choose One of the following letters: A, B or C: ");//Asks the User for his input
        System.out.print("Selection: ");
        Scanner sc = new Scanner(System.in); //Accepts the Users input
        String LetterSelection = sc.nextLine();
        methodswitch(LetterSelection);
     //The Purpose of this condition is to require the user to enter A, B or C and loop until the condition is satisfied.
 
        //This will require the user to enter his name and the string inputted will be stored in the variable 'name'
        System.out.print("Enter your first name: ");
        String name = sc.nextLine();
 
        //This will require the user to enter his age and the integer inputted will be stored in the variable 'age'
        System.out.print("Enter your Age: ");
        int age = sc.nextInt();
 
        //Outputs the information collected in the variables
        System.out.println("");
        System.out.println("Thank You!");
        System.out.println("Your name is: " + name);
        System.out.println("You are " + age + " years old");
        System.out.println("You selected the letter: " + LetterSelection);
 
 
    }
 
    public static void methodswitch(String LetterSelection) {
 
       switch(LetterSelection){
 
       case "A" : 
       case "a" : LetterSelection = LetterSelection; break;
       default : inputMethod(LetterSelection);
 
    }
 
 
  }
 
  public static String inputMethod (String LetterSelection) 
   {
 
 
     System.out.println("____________________________________________________________________________");
     System.out.println("Invalid Selection -- Please Choose One of the following letters: A, B or C: ");//Asks the User for his input
     System.out.print("Selection: ");
     Scanner sc = new Scanner(System.in);
     LetterDelection = sc.nextLine();
 
 
 
     return LetterSelection;
  }
}

I tried this. same thing happens. Why dont the methods return the variable? I'm a bit lost

--- Update ---

I know there arent options, Im trying to get the program to work...

I want the methods to return the variable LetterSelection, back into the the main method so that I could display the letter

In Java, variable and method names begin with lowercase letters, camelCased thereafter. Class names are capitalized and then camelCased. "methodswitch()" should be called "methodSwitch()," and throughout "LetterSelection" should be named "letterSelection." Not following basic Java naming conventions makes your colde more difficult to read and understand.

Comments would also be helpful. What is the intended purpose of methdSwitch()? It looks like a half-written input validation method. Half written because it doesn't consider the user's entry of B/b or C/c. Further, the default case can continue to accept and return invalid entries. No validation is enforced within the method.

In order to use a value returned by a method, it must be assigned to another variable, as in:

String validSelection = methodSwitch( letterSelection );

Good luck!

Originally Posted by melki0795

I want the methods to return the variable LetterSelection, back into the the main method so that I could display the letter

But that's not what it is doing:

public static void methodswitch(String LetterSelection)

The 'void' part of this method declaration means "I don't return anything". However this isn't the big issue with your code. Take a close look at your inputMethod

 public static String inputMethod (String LetterSelection) 
 {
    //snip
     return LetterSelection;
}

It is accepting the String 'LetterSelection' as a parameter and then returning it, without ever actually doing anything (also as Greg noted you should use camelCase for variables and methods to conform with Java conventions).

Confusingly enough, this doesn't even matter because 'inputMethod' is never called. You are defining a variable elsewhere with the identical name of 'LetterSelection'

String LetterSelection = sc.nextLine();

As this thread has progressed I've noticed a tendency to add code when a problem occurs at the expense of the structure and logic flow. Remember what I said about pseudocode? It's so important. Take a step back and think about what your program is supposed to do.

- Welcome the user
- Ask the user for a letter 'A', 'B' or 'C'
- If the letter is not 'A', 'B' or 'C' go back and ask again
- Ask the user for their name
- Ask the user for their age
- Print the letter, the name and age

Changing the code in previous/earlier posts also makes the conversation more difficult. When I copied the code, methodSwitch() was not a void method. If you want to post updated code, post it on its own rather than revising history.

 
 
import java.util.Scanner;
public class Interrogator3
{
  public static void main(String[] args) {
 
 
 
        //Welcoming Message
        System.out.println("Welcome to the program! ");
        System.out.println("");
 
        //The user will be asked to enter his letter of choice.
        System.out.println("Please Choose One of the following letters: A, B or C: ");//Asks the User for his input
        Scanner sc = new Scanner(System.in);
 
        String Letter = sc.nextLine();
        String validLetter = methodswitch(sc, Letter);
        //The Purpose of this condition is to require the user to enter A, B or C and loop until the condition is satisfied.
 
        //This will require the user to enter his name and the string inputted will be stored in the variable 'name'
        System.out.print("Enter your first name: ");
        String name = sc.nextLine();
 
        //This will require the user to enter his age and the integer inputted will be stored in the variable 'age'
        System.out.print("Enter your Age: ");
        int age = sc.nextInt();
 
        //Outputs the information collected in the variables
        System.out.println("");
        System.out.println("Thank You!");
        System.out.println("Your name is: " + name);
        System.out.println("You are " + age + " years old");
        System.out.println("You selected the letter: " + validLetter);
 
 
    }
 
  public static String methodswitch(Scanner sc ,String Letter) {  
 
      String validLetter = "";
 
 
        switch(Letter){
 
         case "A" : 
         case "a" :  validLetter = "a"; break;
 
         default :
            {
                System.out.println("____________________________________________________________________________");
                System.out.println("Invalid Selection -- Please Choose One of the following letters: A, B or C: ");//Asks the User for his input
 
                Letter = sc.nextLine();
                methodswitch(sc, Letter);
            }
        }
        System.out.println("*"+validLetter);
 
      return validLetter;   
 
    }
 
}

https://dl.dropboxusercontent.com/u/6055003/Capture.PNG


As you can see, when I output what im trying to return back, it starts off with A... (how it should be) then the variable (validLetter) goes blank....

hmm... any ideas why this is happening?

I recommend you rethink your design/logic flow as Christopher suggested. And why are B/b and C/c still not considered valid responses?

I'll try doing that... Will a flowchart be more helpful?

--- Update ---

Theyre Not considered as valid responses because I'm trying to get the program to work. I know that the program can work by something similer to the first code i had used in this thread.... But the question requires me to Include A to F and i think by listing them down as 1 condition would be unprofessional.

I'm talking about this piece of code

 
if (!Selection.equals("A") & !Selection.equals("B") & !Selection.equals("C")){

i think that listing a statement something like that all the way to F would be messy....
that's why im thinking of using a switch statement...