Understanding selection

[Chris Caretti]

I am very early into studying Java and using a book called "Java in Two Semesters - 2nd Ed". The early exercises don't have answers and I have been attempting a short programming exercise without success. I do not understand how to build in selection that can be pulled together as a total at the end. The chapter was covering if..else and switch.

Could someone please provide the pseudocode to the following as this might help me work it out?

"Write a program to take an order for a computer system. The basic system costs 375.99. The user then has to choose from a 38cm screen (75.99) or a 43cm screen (99.99). There are also two optional extras DVD/CD Writer (65.99); Printer (125.00). Allow the user to select from these extras and then display the final cost of the order."

[Campbell Ritchie]

Welcome to JavaRanch

We don't simply hand out answers; read this FAQ. It looks a rather awkward example to me, but I think you want an if-else for the printer and if-else for the DVD writer, and you could consider a switch for the screen.
In the switch, how about some sort of error message for the "default."

[Chris Caretti]

Thank you for directing me to the Beginners FAQ. Quite right too! I understand that you wish to see whether I have spent some time on this and tried to construct it myself.

Below is approx. my 8th attempt. I certainly don't wish anyone to provide me with the answer, just some clarity on working through this kind of problem.

I have decided that I want to try and make it work with if..else (and will then use switch once I have understood), so I learn to break down the logical steps properly.

I have been attempting as below. But each time I try it, I can't get it to work so that a value is retained and then all added together at the end.


<blockquote>code:

---

<pre name="code" class="core">package ordersystem;

import java.util.*;

public class OrderSystem {

public static void main(String[] args) {

int screens;
double priceDVD, pricePrinter, price38, price43, subTotal, priceTotal;
char reply;

Scanner sc = new Scanner(System.in);
System.out.println("Choose your screen size (38/43) ");
screens = sc.nextInt();

price38 = 451.98;
price43 = 475.98;


if (screens == 38) {
System.out.println("Thank you, your subtotal is:� " + 451.98);
} else if (screens == 43) {
System.out.println("Thank you, your subtotal is:� " + 475.98);
}

System.out.println("Would you like extras?(y/n)?");
reply = sc.next().charAt(0);

priceDVD = 65.99;
pricePrinter = 125.00;

if (reply == 'y') {
System.out.println("Please select from the following");
System.out.println("[1] DVD at �65.99");
System.out.println("[2] Printer at �125.00");
System.out.println("[3] DVD and Printer at �190.99");

reply = sc.next().charAt(0);

if (reply == '1') {
System.out.println(" ")
}
}

}
}</pre>

---

</blockquote>
[edit]Add Code Tags. CR[/edit]
[ July 16, 2008: Message edited by: Campbell Ritchie ]

[Campbell Ritchie]

It is (as I said before) awkward; I think this is intentional to force you to use both if-elses and switches.

You seem to be making good progress however.

For your latter selection where you have 1 2 3 you might find the Scanner#nextInt method easier to use. After that selection, you are not printing out the total price. But the 1 2 3 format lends itself to a switch.

I suggest you add an else to the bit about screen size for what happens if you don't enter 38 or 43.
You will have problems with Exceptions if you enter something which isn't a number, but you will probably study Exceptions in a few weeks' time.

[Chris Caretti]

Thank you for your advice so far, and I have been attempting to understand where I am going wrong. Below is my latest attempt. I am using both if..else and switch, but am not sure if I have set the costs in the best way. Also it does not end the right way on some selections. It is going back to the earlier question on extras.

I guess my two questions here are, how should I be incorporating the else part so the total cost is delivered at the end? And secondly, is there a better way to establish those costs in the first place?

package ordersystem3;
 
import java.util.*;
 
public class OrderSystem3 {
 
    public static void main(String[] args) {
        //definitions are assigned first
        int screens;
        double system38, system43, extraDVD, extraPrinter, subTotal, priceTotal1, priceTotal2, priceTotal3, priceTotal4, priceTotal5, priceTotal6;
        char reply, combination;
 
        system38 = +451.98;
        system43 = +475.98;
        extraDVD = +65.99;
        extraPrinter = +125.00;
        priceTotal1 = system38 + extraDVD;
        priceTotal2 = system38 + extraPrinter;
        priceTotal3 = system38 + extraDVD + extraPrinter;
        priceTotal4 = system43 + extraDVD;
        priceTotal5 = system43 + extraPrinter;
        priceTotal6 = system43 + extraDVD + extraPrinter;
 

        Scanner sc = new Scanner(System.in);
        System.out.println("What size screen would you like? (38/43) ");
        screens = sc.nextInt();
 
        if (screens == 38) {
            System.out.println("Thank you, your subtotal is:� " + system38);
        }
        System.out.println("Would you like extras?(y/n)?");
 
        reply = sc.next().charAt(0);
 
        if (reply == 'y') {
 
            System.out.println("Please select from the following");
            System.out.println("[1] DVD at �65.99");
            System.out.println("[2] Printer at �125.00");
            System.out.println("[3] DVD and Printer at �190.99");
            System.out.println();
 
            combination = sc.next().charAt(0);
 
            switch (combination) {
                case '1':
                    System.out.println("Thank you, your total is:� " + priceTotal1);
                    break;
                case '2':
                    System.out.println("Thank you, your total is:� " + priceTotal2);
                    break;
                case '3':
                    System.out.println("Thank you, your total is:� " + priceTotal3);
                    break;
                default:
                    System.out.println("No such combination");
            }
        } else {
            System.out.println("Thank you, your total is:� " + system38);
        }
        if (screens == 43) {
            System.out.println("Thank you, your subtotal is:� " + system43);
        }
        System.out.println("Would you like extras?(y/n)?");
 
        reply = sc.next().charAt(0);
 
        if (reply == 'y') {
 
            System.out.println("Please select from the following");
            System.out.println("[1] DVD at �65.99");
            System.out.println("[2] Printer at �125.00");
            System.out.println("[3] DVD and Printer at �190.99");
            System.out.println();
 
            combination = sc.next().charAt(0);
 
            switch (combination) {
                case '1':
                    System.out.println("Thank you, your total is:� " + priceTotal3);
                    break;
                case '2':
                    System.out.println("Thank you, your total is:� " + priceTotal4);
                    break;
                case '3':
                    System.out.println("Thank you, your total is:� " + priceTotal5);
                    break;
                default:
                    System.out.println("No such combination");
            }
        }
    }
}
   

[Nathan Leniz]

A question. Since the user must select a screen size, wouldn't it be easier to ask the questions about the extras only once? Also, instead of defining all the ending values, couldn't you have a working total variable that you alter based on input, then display that total?

[Chris Caretti]

Yes, your questions mirror my desire exactly. However, my ability so far and lack of understanding have led me to follow the wordy route I've currently arrived at!

[Nathan Leniz]

I'm not saying that my thinking is the best way, not even remotely, but this is how I'd think about solving the problem.

  
// Define my variables and give them values. Also make a variable to keep a track of the total.
 
variables = individual values
total = baseCost; //it must be at least equal to this
 
Get input from the user for their screen size selection.
Add that value to the total.
 
Would the user like any extras?
If (if they do)
{
    Here are the available extras, which would you like?
    Get user input.
    Adjust the total based on the selection
}
 
Display the total
  

[Chris Caretti]

Many thanks for your help. It really helped me think it through more clearly. Below is where I have got to. Do you think this is succinct enough based on the parameters I was required to work within?

One final thing, I have noticed that if the user enters an incorrect choice, then whilst a message can be displayed it doesn't return them to the preceding question? is this because I'm missing something, or the way the if..else is nested?

package ordersystem3_1;
 
import java.util.*;
 
public class OrderSystem3_1 {
 
    public static void main(String[] args) {
 
        //define variables and give values
        int screens;
        double systemTotal;
        char reply, combination;
 
        double baseSystem = 375.99;
        double screen38 = 75.99;
        double screen43 = 99.99;
        double extraDVD = 65.99;
        double extraPrinter = 125.00;
 
        systemTotal = baseSystem;
 
        //get input from the user for their screen selection
 
        Scanner sc = new Scanner(System.in);
        System.out.println("What size screen would you like? (38/43) ");
        screens = sc.nextInt();
 

        if (screens == 38) {
            systemTotal += screen38;
            System.out.println("Thank you, your subtotal is:� " + systemTotal);
        } else if (screens == 43) {
            systemTotal += screen43;
            System.out.println("Thank you, your subtotal is:� " + systemTotal);
        }
 
        System.out.println("Would you like extras?(y/n)?");
        reply = sc.next().charAt(0);
 
        if (reply == 'y') {
 
            System.out.println("Please select from the following");
            System.out.println("[1] DVD at �65.99");
            System.out.println("[2] Printer at �125.00");
            System.out.println("[3] DVD and Printer at �190.99");
            System.out.println();
 
            combination = sc.next().charAt(0);
 
            switch (combination) {
                case '1':
                    systemTotal += extraDVD;
                    System.out.println("Thank you, your total is:� " + systemTotal);
                    break;
                case '2':
                    systemTotal += extraPrinter;
                    System.out.println("Thank you, your total is:� " + systemTotal);
                    break;
                case '3':
                    systemTotal += extraDVD + extraPrinter;
                    System.out.println("Thank you, your total is:� " + systemTotal);
                    break;
                default:
                    System.out.println("No such combination");
            }
        } else if (reply == 'n') {
 
            System.out.println("Thank you, your total is:� " + systemTotal);
        }
    }
}

[Nathan Leniz]

The only thing I can see is you could easily cut down on your println() statements. In both your if/else and switch blocks, no matter what you alter the value with, you still print the user's subtotal.

Ah, forgot to add...

If you are expecting only two inputs and nothing else, you can catch that input before executing through the rest of your program, and repeat the catching until the user enters something valid.

  
while (Not((User Input matches 38) OR (User Input matched 43)))
{
"User, please enter a valid selection"
//Get some user input here that while can use
}
 
  

[ July 21, 2008: Message edited by: Nathan Leniz ]