Why is this if-statement triggering in this While-loop?

Question

I'm new to Java, and I am creating a while-loop with one of the conditions being:

if ((userChoice != 'p') || (userChoice != 'P') || (userChoice != 's') || (userChoice != 'S')) System.out.println("*** Use P or S, please. ***");

Why is it that when I enter "p","P", "s", or "S" the program still outputs ""* Use P or S, please. *"??

This is the whole program:

import java.util.Scanner;

public class Foothill
{
   public static void main(String[] args)
   {
      // declare an object that can be used for console input
      Scanner inputStream = new Scanner(System.in);

      // declare variables
      String strUserInput;
      char userChoice, userCredits;
      int numYogurts, yogurtWallet = 0;
      // while loop for full transaction
      while (true)
      {
      // menu message
          System.out.println("Menu: \n P (process Purchase) \n S (Shut down)");
          strUserInput = inputStream.nextLine();
          userChoice = strUserInput.charAt(0);

        // condition that forces users to select only P or S
          if ((userChoice != 'p') || (userChoice != 'P') || (userChoice != 's') || (userChoice != 'S'))
              System.out.println("*** Use P or S, please. ***");

          System.out.println("Your choice:" + userChoice);
        // if condition that starts purchase part of transaction
          if ( (userChoice == 'p') || (userChoice == 'P') ) 
          {
              System.out.println("How many yogurts would you like to buy?");
              strUserInput = inputStream.nextLine();
              numYogurts = Integer.parseInt(strUserInput);

              yogurtWallet += numYogurts;

              System.out.println("You just earned " + numYogurts + " stamps and have a total of " + yogurtWallet + " to use");
              // if condition that tests number of purchased yogurts
              if (yogurtWallet >= 10)
              {
                  System.out.println("You qualify for a free yogurt. Would you like to use your credits? (Y or N)");
                  strUserInput = inputStream.nextLine();
                  userCredits = strUserInput.charAt(0);

                  if ((userCredits == 'Y') || (userCredits == 'y'))
                  {
                      yogurtWallet -= 10;
                      System.out.println("You have just used 10 credits and have " + yogurtWallet + " left. Enjoy your free yogurt.");
                  }
              }
          } 
          // if condition that stops the program 
          if ( (userChoice == 's') || (userChoice == 'S') )
          {
              System.out.println("Goodbye!");
              break;
          }

      }
   }
}

What does || do?

Sotirios Delimanolis
– Sotirios Delimanolis

2013-10-27 16:31:42 +00:00
Commented Oct 27, 2013 at 16:31 — Sotirios Delimanolis
– Sotirios Delimanolis, Commented Oct 27, 2013 at 16:31
Change the || to && and it will work

sara
– sara

2013-10-27 16:33:22 +00:00
Commented Oct 27, 2013 at 16:33 — sara
– sara, Commented Oct 27, 2013 at 16:33

Maroun · Accepted Answer · 2013-10-27 16:34:55Z

4

Assume you entered p. Due to Short Circuit Evaluation, Java will continue and check all the conditions inside the if statement, the next check is != 'P', which is true! The same holds for the other inputs:

userChoice |  != 'p' | != 'P' | != 's' | != 'S'
-----------+---------+--------+--------+-------
    p      |   Yes   |   --   |   --   |  --
    P      |   No    |   Yes  |   --   |  --
    s      |   No    |   No   |   Yes  |  --
    S      |   No    |   No   |   No   |  Yes

-- means not evaluated because of Short Circuit Evaluation.

So in all cases, your if is satisfied!

answered Oct 27, 2013 at 16:34

Maroun

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3 Comments

user2173738 Over a year ago

shot-circuit condition is the OPs issue and placeholder for bugs.

Maroun Over a year ago

@nikpon Yes. That's what I clarified.

user2173738 Over a year ago

It will not check all conditions, it will output after the first due to true.

sdanzig · Accepted Answer · 2013-10-27 16:33:57Z

1

No matter which letter you choose, it will still be not equal to the other choices. || means OR. So in A OR B, if A is true, or B is true, then the entire condition is true. What you need to do is use &&, for AND.

answered Oct 27, 2013 at 16:33

sdanzig

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1 Comment

user2173738 Over a year ago

A = B not equal to B = A the logic is not a Java but Java has logical operations.

Saurabh Batra · Accepted Answer · 2013-10-27 16:34:14Z

0

use if ((userChoice != 'p') && (userChoice != 'P') && (userChoice != 's') && (userChoice != 'S'))

This will solve your issue.

answered Oct 27, 2013 at 16:34

Saurabh Batra

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1 Comment

Saurabh Batra Over a year ago

can you please make it a practice to accept the answer that you use and works, it might help others too. :)

Paul Samsotha · Accepted Answer · 2013-10-27 16:34:28Z

0

if ((userChoice != 'p') && (userChoice != 'P') && 
   userChoice != 's') && (userChoice != 'S')) 
       System.out.println("*** Use P or S, please. ***");

answered Oct 27, 2013 at 16:34

Paul Samsotha

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