Program repeating switch-case because of inability to get user input again during a loop

Question

I'm almost done with a Java project for an intro class where a user has to perform conversions on a value of gasoline. The program runs fine when I put it through command prompt, up until one point where you select the conversion (from the choices 1, 2, 3, 4, or 5).

What happens is that the program computes it fine, and displays the "Type NO if you want to exit" part just fine, but then it repeats the program before the user has the chance to even type anything. I'm not sure what to do here. I tried typing keyboard.nextLine(); so it would skip to a line that the user could sent input, but the same error happened. If I change the line at the bottom to run the loop while yesOrNo = yes, then it stops the program abruptly. I assume it's the same problem, although I'm not sure what to do and I couldn't find this issue on other forum posts. Thanks anyone who decides to help.

Here's my code, minus the main method / class headers:

    // Ask the user for their name
    System.out.println("What is your name?");

    // Use Scanner to get the user's name (a string variable)
    String name = keyboard.nextLine();

    // Welcome the user by name & give a readable description of the program using escape sequences
    System.out.println(name + ", welcome. I am Rachel and this program will help you perform gasoline analysis.\n");
    System.out.println("Using this program, you can extract information about any amount of gallons of gasoline, such as:");
    System.out.println("its equivalent in liters, its price, and how much oil is required to produce it, for example.\n");
    System.out.println("Press any letter to continue.");

    String yesOrNo = keyboard.next();
    boolean performConversion = true;


    // Perform the conversions the user wants at least once, until they want to stop. 
    do 
{
        // Get the value of gallons (floating-point value) of gasoline from the user.
            System.out.println("Please enter a number that will represent your gallons of gasoline.");
            double userGallons = keyboard.nextDouble();

        // Declare variables and convert the gallons to the other units of measurement. 
            double liters = (userGallons * 3.7854);

            double barrelsNeeded = (userGallons / 19.5);

            double poundsCO2 = (userGallons * 20.0);

            double ethanolEnergy = (userGallons * 75700);

            double price = (userGallons * 4.0);

        // Show the user a menu of their choices for conversion.
            System.out.println("Select the conversion you would like to perform here:");
            System.out.println("Press 1 for liters");
            System.out.println("2 for pounds of CO2 produced");
            System.out.println("3 for equivalent energy amount of ethanol gallons");
            System.out.println("4 for price in USD");
            System.out.println("or 5 for barrels of oil required to produce that amount of gasoline.");
            int userChoice = keyboard.nextInt();

        // Display the original gallons and the available conversions to the user. 

        switch(userChoice)
        {
            case 1:
                System.out.println("Original gallons of gasoline: " + userGallons + "gallons");
                System.out.println("Amount in liters: " + liters);
                System.out.println("Type NO if you want to exit, or any other key to continue.");
                break;
            case 2:
                performConversion = true;
                System.out.println("Original gallons of gasoline: " + userGallons + "gallons");
                System.out.println("Pounds of CO2 produced : " + poundsCO2);
                System.out.println("Type NO if you want to exit, or any other key to continue.");
                break;
            case 3:
                performConversion = true;
                System.out.println("Original gallons of gasoline: " + userGallons + "gallons");
                System.out.println("Equivalent energy amount in ethanol gallons: " + ethanolEnergy + " BTU");
                System.out.println("Type NO if you want to exit, or any other key to continue.");
                break;
            case 4:
                performConversion = true;
                System.out.println("Original gallons of gasoline: " + userGallons + "gallons");
                System.out.println("Price in USD: $" + price);
                System.out.println("Type NO if you want to exit, or any other key to continue.");
                break;
            case 5:
                performConversion = true;
                System.out.println("Original gallons of gasoline: " + userGallons + "gallons");
                System.out.println("Number of barrels of oil needed to produce that amount of gallons: " + barrelsNeeded);
                System.out.println("Type NO if you want to exit, or any other key to continue.");
                break;
            default:
                System.out.println("Invalid character. Please enter 1, 2, 3, 4, or 5.");
        }
    } while (!"no".equalsIgnoreCase(yesOrNo));
    System.out.println("Goodbye! The program will now end.");
}

}

You're never changing the value of variable yesOrNo inside the loop, so that "while" condition just keeps going. Maybe add an extra clause so if they enter 0 gallons you set it to "no"? — racraman, Feb 01 '19 at 04:04

score 0 · Answer 1 · answered Feb 01 '19 at 04:16

0

Without doing any restructuring, you could change your while condition thusly:

} while (!"no".equalsIgnoreCase(keyboard.next()) );

answered Feb 01 '19 at 04:16

glumplum

133
7

Thank you! That worked, I was killing myself trying to do that but really it was way simpler than I thought... – Rachel Feb 01 '19 at 17:01

score 0 · Answer 2 · answered Feb 01 '19 at 04:42

Since you want the conversion to happen at least once, I suggest you should move these two statements(mentioned below) inside the do { //... } while(); loop, at the very end (i.e. after the switch...case statement):

System.out.println("Press any letter to continue.");

String yesOrNo = keyboard.next();

Reason

What you are trying to achieve is for the user to perform the conversion, then after they are given a choice of whether to continue or not.

The current program doesn't ask the user for this choice. Instead, it just loops on using the value of the yesOrNo variable, which was set prior to entering the loop.

Keeping the aforementioned statements at the very end of the loop should give you your desired results.

Also, I see that you've created a variable performConversion, however it is never used somewhere (at least not in the code snippet provided). Therefore, unless this variable is used somewhere else in the main() method, I suggest you remove it.

Program repeating switch-case because of inability to get user input again during a loop

2 Answers2