nested do while loop in java

Question

I'm writing a simple calculator in java where you can perform 4 basic operations with only 2 operands. What i need is that inside the if statement I want to perform a loop where a user will continue doing the same operation when ask to continue and if it quits it will be ask again to continue by selecting another operations. My problem is that it is not performing a loop inside the if statements instead it performs a loop where a user is ask to continue by selecting another operations.

import java.util.Scanner;

public class calculator
{





public static void main(String [] args)
{
    Scanner input = new Scanner (System.in);
    double x, y;
    double operation;
    String getChar;
    String chooseOperation;

    do
    {   
        System.out.println("Choose your operation:");
        System.out.println("A. Addition");
        System.out.println("B. Subraction");
        System.out.println("C. Multiplication");
        System.out.println("D. Division");

        chooseOperation = input.nextLine();

        if ((chooseOperation.equals("A")) | (chooseOperation.equals("a")))
        {
            do
            {
                System.out.println("You Choose Addition\n\n\n");
                System.out.println("Input the first number:\n");
                x = input.nextDouble();
                System.out.println("Input the second number:\n");
                y = input.nextDouble();
                operation = x+y;
                System.out.println("The sum is :"+operation);

                System.out.println("Continue?");
                System.out.println("Y/N");
                getChar=input.nextLine();
            }while(getChar.equals("Y"));
        }

        else if ((chooseOperation.equals("B")) | (chooseOperation.equals("b")))
        {
            do
            {
                System.out.println("You Choose Subtraction\n\n\n");
                System.out.println("Input the first number:\n");
                x = input.nextDouble();
                System.out.println("Input the second number:\n");
                y = input.nextDouble();
                operation = x-y;
                System.out.println("The difference is :"+operation);

                System.out.println("Continue?");
                System.out.println("Y/N");
                getChar=input.nextLine();
            }while(getChar.equals("Y"));
        }

        else if ((chooseOperation.equals("C")) | (chooseOperation.equals("c")))
        {
            do
            {
                System.out.println("You Choose Multiplication\n\n\n");
                System.out.println("Input the first number:\n");
                x = input.nextDouble();
                System.out.println("Input the second number:\n");
                y = input.nextDouble();
                operation = x*y;
                System.out.println("The product is :"+operation);

                System.out.println("Continue?");
                System.out.println("Y/N");
                getChar=input.nextLine();
            }while(getChar.equals("Y"));
        }

        else if ((chooseOperation.equals("D")) | (chooseOperation.equals("d")))
        {
            do
            {
                System.out.println("You Choose Division\n\n\n");
                System.out.println("Input the first number:\n");
                x = input.nextDouble();
                System.out.println("Input the second number:\n");
                y = input.nextDouble();
                operation = x/y;
                System.out.println("The quotient is :"+operation);

                System.out.println("Continue?");
                System.out.println("Y/N");
                getChar=input.nextLine();
            }while(getChar.equals("Y"));
        }
        else
        {
            System.out.println("Invalid Selection!\n\n\n");
        }
        System.out.println("Do you want to continue?\n\nY/N");
        getChar=input.nextLine();
    }while((getChar.equals("Y"))|(getChar.equals("y")));

}    
}

please cut down the code to the part where you have trouble with — Ben Win
– Ben Win, Commented Sep 18, 2014 at 12:28
What is the input that you are giving when you are testing your program? Do you type Y or y? — Simon
– Simon, Commented Sep 18, 2014 at 12:30
if your referring to the loop in if statements, it's Y since i'm having trouble giving it a boolean expression which involves bitwise operators — David Diaz
– David Diaz, Commented Sep 18, 2014 at 12:36
(to the questioners) Just run the program with A , 6, 7 and you see the problem. There is something wrong with input.nextLine(). It gets skipped... — Robert
– Robert, Commented Sep 18, 2014 at 12:40
@OhemgiIstalLes you can refer to the do while loops inside the if...else statements. The computer is suppose to ask you if you want to continue doing the same operations but instead it cancelled the loops — David Diaz
– David Diaz, Commented Sep 18, 2014 at 12:40

ortis · Accepted Answer · 2014-09-18 12:44:06Z

1

Read the entire line every time then parse into double:

          //Addition
          do
            {
                System.out.println("You Choose Addition\n\n\n");
                System.out.println("Input the first number:\n");
                x = Double.parseDouble(input.nextLine());//read the whole line, then parse into double
                System.out.println("Input the second number:\n");
                y = Double.parseDouble(input.nextLine());//read the whole line, then parse into double
                operation = x + y;
                System.out.println("The sum is :" + operation);

                System.out.println("Continue?");
                System.out.println("Y/N");
                getChar = input.nextLine();//when not reading the whole line, getChar is empty
            }
            while (getChar.equals("Y"));

Otherwise, getCharseem to contain the next line character created when user input the numbers (type the number then press Enter).

edited Sep 18, 2014 at 12:44

answered Sep 18, 2014 at 12:39

ortis

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6 Comments

David Diaz Over a year ago

is there a package in using the double.parseDouble?

ortis Over a year ago

it's Double.parseDouble, not double.parseDouble. It's part of the default Java framework java.lang.Double

David Diaz Over a year ago

thanks for your help it work!! can you tell me how does the java.lang.Double functions. i'm still a student by the way with a hearing impaired problem so i'm not that good in listening the advice of my professors. how about showing me a link instead.

Robert Over a year ago

here you go. docs.oracle.com/javase/7/docs/api/java/lang/… As ortis wrote, the problem with input.nextDouble(); is that there is still a "new line sign" in the line afterwards so with the next input.nextLine(); you are reading that and not asking the user for a new input.

ortis Over a year ago

In addition to the link Robert gave you, you can check out the source code of the Double.parseDouble method but that might be a litte complex for a beginner. grepcode.com/file/repository.grepcode.com/java/root/jdk/openjdk/…

|

ortis · Accepted Answer · 2014-09-18 13:10:42Z

0

Its a long time ago I programmed java. But I think its because you're using only one |. I'm not sure but I thought java needs two |. So your first if will be:

if (chooseOperation.equals("A") || chooseOperation.equals("a"))
{

}

edited Sep 18, 2014 at 13:10

ortis

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answered Sep 18, 2014 at 12:40

Vincent Beltman

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3 Comments

David Diaz Over a year ago

actually I applied that "||" instead of "|" using the same concept i've learned in c++ but i"m getting an error so i only use "|"

ortis Over a year ago

In this example, using | or || makes no difference (except, maybe, for execution speed).

Narmer Over a year ago

The operators | and & are not only bitwise operators (when applied to integer arguments), but also non-short-circuiting logical operators that evaluate both operands regardless of the value of the first

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