Please help with methods!

Question

hello
i have a problem that i have been working on for a few days now. i have just started to learn about methods and how to use them. my first attempt has met with a few problems however. i was to make a calculator with a menu that did the four basic math operations. i have done that and the program is working perfectly. the only trouble is that i was to have 7 methods and i only have 6. this is how i was supposed to split it up
4 for operations
1 for number prompt and input
1 for menu
1 for output of results
i am at a lost for how to put the outputs in ONE method. can anyone please help me. i realize i am using an unfamiliar console, but ican send it to you if you contact me. then you can test it out here is the program:
import java.io.*;
import java.awt.*;
import hsa.Console;
import java.text.*;
public class calculator
    //Variable declaration -- defined global because they can be utilized by all methods
    static double num, num1, num2, mult, div, add, subtract;
    static int choice;
    static Console c;
    public static void main (String[] args)
        //variable initialization
        c = new Console ();
        num = 0;
        mult = 0;
        div = 0;
        add = 0;
        subtract = 0;
        num1 = input (num);
        num2 = input (num);
        do
            c.println ("\t\t Main Menu");
            c.println ("\t\t 1. Multiply the numbers");
            c.println ("\t\t 2. Divide the 1st by the 2nd number");
            c.println ("\t\t 3. Add the two numbers");
            c.println ("\t\t 4. Subtract the 2nd from the 1st number");
            c.println ("\t\t 5. End");
            do
                c.print ("What is your choice (1-5): ");
                choice = c.readInt ();
                if ((choice < 1) || (choice > 5))
                    c.println ("Invalid...enter 1-5 only");
            while ((choice < 1) || (choice > 5));
            switch (choice)
                case 1:
                    multiply (num1, num2, mult);
                    break;
                case 2:
                    divide (num1, num2, div);
                    break;
                case 3:
                    add (num1, num2, add);
                    break;
                case 4:
                    subtract (num1, num2, subtract);
                    break;
        while (choice != 5);
        c.println ("\n\nThanks for using my calculator. Bye.....");
    //method used to input the 2 numbers
    public static double input (double num)
        c.setTextColor (Color.cyan);
        c.print ("Please enter a number: ");
        num = c.readDouble ();
        return num;
    //method used to multiply
    public static double multiply (double num1, double num2, double mult)
        DecimalFormat z = new DecimalFormat ("##,###,##0.00");
        mult = (num1 * num2);
        c.setTextColor (Color.red);
        c.println ("The numbers multiplied equals: " + z.format (mult));
        return mult;
    //method used to divide
    public static double divide (double num1, double num2, double div)
        DecimalFormat z = new DecimalFormat ("##,###,##0.00");
        //if ( num2 = 0 );
        //c.println("You can not divide by zero");
        div = (num1 / num2);
        c.setTextColor (Color.red);
        c.println ("The 1st number divided by the 2nd number equals: " + z.format (div));
        return div;
    //method used to add
    public static double add (double num1, double num2, double add)
        DecimalFormat z = new DecimalFormat ("##,###,##0.00");
        add = (num1 + num2);
        c.setTextColor (Color.red);
        c.println ("The numbers added equals: " + z.format (add));
        return add;
    //method used to subtract
    public static double subtract (double num1, double num2, double subtract)
        DecimalFormat z = new DecimalFormat ("##,###,##0.00");
        subtract = (num1 - num2);
        c.setTextColor (Color.red);
        c.println ("The 2nd number subtracted from the 1st equals: " + z.format (subtract));
        return subtract;
}Thanks

Answer 1

Tradeoff wrote:
the only trouble is that i was to have 7 methods and i only have 6. this is how i was supposed to split it up
4 for operations
1 for number prompt and input
1 for menu
1 for output of results
i am at a lost for how to put the outputs in ONE method. can anyone please help me.You can solve a problem in many ways, and when you design a class the number of methods used may vary from solution to solution. But it seems likely in this case that your teacher expected the operations to be:
4 for operationsSo, after getting two numbers from the user, perform the operation and return the result. Note that this means that the operation methods would take TWO parameters, not three as you've been doing.
1 for number prompt and inputOK. This would not take a number as a parameter, so you've done that wrong.
1 for menuYou haven't done that part yet. You've stuck that stuff into the main method. You're probably supposed to create seven methods in addition to the main method.
1 for output of resultsSo, print the number that's the result of the operation. This is the number that's been returned by the operation, which you're ignoring in your code.
Of course, if you're confused about the assignment, you should ask your teacher, not here. We can't read your teacher's mind. Like I said there are lots of ways to solve a problem and they might not all be the same way your teacher had in mind.
You seem to be confused about the whole idea of functions and return values. If you want a method to act as a function -- that is, to operate on its arguments and return a result without side effects -- then you don't pass the result value as a variable. You do this:
double result = someOperation(arg1, arg2);and not this, as you have been doing:
double result = someOperation(arg1, arg2, result);The latter case makes no sense. The method only gets a copy of "result" when the method is called, so any changes to it are lost except for what it returns. Do it like the former example above.