Functions Part 2

110. Keychains for Sale, real ultimate power - Link

Task
Code

You’re going to add some error checking and additional features, to Keychains2.You need to make sure that the user always has a positive number, or 0, of keychains in the order.You need to check for a valid menu choice. If not, display an error message and show the menu again.You will need 3 new variables in main, one to store the sales tax (8.25%), one to store the shipping cost per order (

5.00), and one to store the additional per keychain shipping cost (

1.00).view_order() will need to be passed the three additional variables, a total of five, and have a return type of void. It will display, on different lines, the number of keychains in the order, the price per keychain, the shipping charges on the order, the subtotal before tax, the tax on the order, and the final cost of the order.view_order() might look like public static void view_order( int num_keychains, double price_per_keychain, double tax, int base_shipping, int per_keychain_shipping )checkout() will need to be passed the same values as view_order(), and have a return type of void. It will ask the user for his/her name in order to deliver them correctly, then call view_order() to display the order information, and then thank the user, by name, for ordering.Sample Output

Ye Olde Keychain Shoppe

1. Add Keychains to Order
2. Remove Keychains from Order
3. View Current Order
4. Checkout

Please enter your choice: 1

You have 0 keychains. How many to add? 3
You now have 3 keychains.

1. Add Keychains to Order
2. Remove Keychains from Order
3. View Current Order
4. Checkout

Please enter your choice: 2

You have 3 keychains. How many to remove? 1
You now have 2 keychains.

1. Add Keychains to Order
2. Remove Keychains from Order
3. View Current Order
4. Checkout

Please enter your choice: 3

You have 2 keychains.
Keychains cost $10 each.
Shipping charges are $5.00.
Subtotal before tax is $20.00.
Tax on the order is $1.65.
Total cost is $26.65.

1. Add Keychains to Order
2. Remove Keychains from Order
3. View Current Order
4. Checkout

Please enter your choice: 4

CHECKOUT

What is your name? Biff
You have 2 keychains.
Keychains cost $10 each.
Shipping charges are $5.00.
Subtotal before tax is $20.00.
Tax on the order is $1.65.
Total cost is $26.65.
Thanks for your order, Biff!

Keychains3.java

import java.util.Scanner;

public class Keychains3
{
    public static void main( String[] args )
    {
        Scanner keyboard = new Scanner(System.in);
        int choice;
        int keychains = 0;
        double price = 10;
        double tax = 0.0825;
        double shipping = 5;
        double perShipping = 1;

        System.out.println("Ye Olde Keychain Shoppe\n");

        do
        {
            System.out.println("1. Add Keychains to Order");
            System.out.println("2. Remove Keychains from Order");
            System.out.println("3. View Current Order");
            System.out.println("4. Checkout\n");
            System.out.print("Please enter your choice: ");
            choice = keyboard.nextInt();

            if ( choice == 1 )
            {
                keychains = add_keychains(keychains);
            }
            else if ( choice == 2 )
            {
                keychains = remove_keychains(keychains);
            }
            else if ( choice == 3 )
            {
                view_order(keychains, price, tax, shipping, perShipping);
            }
            else if ( choice == 4 )
            {
                checkout(keychains, price, tax, shipping, perShipping);
            }
            else
            {
                System.out.println("Invalid choice.");
            }
        } while ( choice != 4 );
    }

    public static int add_keychains( int keychains )
    {
        Scanner keyboard = new Scanner(System.in);
        int add;

        System.out.printf("\nYou have %s keychains. How many to add? ", keychains);
        add = keyboard.nextInt();
        keychains += add;
        System.out.printf("You now have %s keychains.\n\n", keychains);

        return keychains;
    }

    public static int remove_keychains( int keychains )
    {
        Scanner keyboard = new Scanner(System.in);
        int remove;

        System.out.printf("\nYou have %s keychains. How many to remove? ", keychains);
        remove = keyboard.nextInt();
        keychains -= remove;
        System.out.printf("You now have %s keychains.\n\n", keychains);

        return keychains;
    }

    public static void view_order( int keychains, double price, double tax, double shipping, double perShipping )
    {
        System.out.printf("\nYou have %s keychains.\n", keychains);
        System.out.printf("Keychains cost $%s each.\n", price);
        System.out.printf("Shipping charges are $%s.\n", shipping);
        System.out.printf("Subtotal before tax is $%s.\n", keychains * price);
        System.out.printf("Tax on the order is $%s.\n", (keychains * price + shipping) * tax);
        System.out.printf("Total cost is $%s.\n\n", (keychains * price + shipping) + (keychains * price + shipping) * tax);
    }

    public static void checkout( int keychains, double price, double tax, double shipping, double perShipping )
    {
        Scanner keyboard = new Scanner(System.in);
        String name;
        System.out.print("\nCHECKOUT\n\n");

        System.out.print("What is your name? ");
        name = keyboard.next();
        System.out.printf("You have %s keychains.\n", keychains);
        System.out.printf("Keychains cost $%s each.\n", price);
        System.out.printf("Shipping charges are $%s.\n", shipping);
        System.out.printf("Subtotal before tax is $%s.\n", keychains * price);
        System.out.printf("Tax on the order is $%s.\n", (keychains * price + shipping) * tax);
        System.out.printf("Total cost is $%s.\n", (keychains * price + shipping) + (keychains * price + shipping) * tax);
        System.out.printf("Thanks for your order, %s!\n", name);
    }
}

111. Calling Functions from Other Files - Link

Task
Code

Rewrite the Weekday Calculator to have almost no functions in it. Start by opening up WeekdayCalculator.java and saving a copy of it as CallingFunctionsFromOtherFiles.java.Then erase all the functions except for main() and weekday().Now, when you compile it, you should get a lot of errors about undefined functions.Then rewrite all the function calls so that they refer to versions in your previous assignments. The functions will be these:

MonthName.month_name()
WeekdayName.weekday_name()
MonthOffset.month_offset()
WeekdayCalculator.is_leap()

import java.util.Scanner;

public class CallingFunctionsFromOtherFiles
{
    public static void main( String[] args )
    {
        Scanner keyboard = new Scanner(System.in);

        System.out.println("Welcome to Mr. Mitchell's fantastic birth-o-meter!");
        System.out.println("All you have to do is enter your birth date, and it will tell you the day of the week on which you were born.");
        System.out.println();
        System.out.println("Some automatic tests....");
        System.out.println("12 10 2003 => " + weekday(12,10,2003));
        System.out.println(" 2 13 1976 => " + weekday(2,13,1976));
        System.out.println(" 2 13 1977 => " + weekday(2,13,1977));
        System.out.println(" 7  2 1974 => " + weekday(7,2,1974));
        System.out.println(" 1 15 2003 => " + weekday(1,15,2003));
        System.out.println("10 13 2000 => " + weekday(10,13,2000));
        System.out.println();

        System.out.println("Now it's your turn!  What's your birthday?");
        System.out.print("Birth date (mm dd yyyy): ");
        int mm = keyboard.nextInt();
        int dd = keyboard.nextInt();
        int yyyy = keyboard.nextInt();

        System.out.println("You were born on " + weekday(mm,dd,yyyy));
    }

    public static String weekday( int mm, int dd, int yyyy )
    {
        int yy, total;
        String date = "";

        yy = yyyy - 1900;
        total = yy / 4;
        total += yy;
        total += dd;
        total += MonthOffset.month_offset( mm );

        if ( WeekdayCalculator.is_leap( yyyy ) && (mm == 1 || mm == 2) )
            total--;

        date = WeekdayName.weekday_name( total % 7 ) + ", " + MonthName.month_name( mm ) + " " + dd + ", " + yyyy;

        return date;
    }
}

112. Evenness Function - Link

Task
Code

Write a function like so:

public static boolean isEven( int n )

The function should return the value true if n is an even number (evenly divisible by 2) and false otherwise.Also, write

public static boolean isDivisibleBy3( int n )

The function should return the value true if n is evenly divisible by 3 and false otherwise.Write a main() that contains a for loop to generate all the numbers from 1 to 20. Use if statements inside the loop to mark the number with a ”<” if it’s even, with a ”=” if it’s evenly divisible by 3, and with both if it’s divisible by both 2 and 3.Sample Output

public class EvennessFunction
{
    public static void main( String[] args )
    {
        for ( int i = 1; i <= 20; i++ )
        {
            if ( isEven(i) )
                System.out.println(i + " <");
            if ( isDivisibleBy3(i) )
                System.out.println(i + " =");
            if ( !isEven(i) && !isDivisibleBy3(i) )
                System.out.println(i);
        }
    }

    public static boolean isEven( int n )
    {
        return ( n % 2 == 0 );
    }

    public static boolean isDivisibleBy3( int n )
    {
        return ( n % 3 == 0 );
    }

}

113. Finding Prime Numbers - Link

Task
Code

Write a function like so:

public static boolean isPrime( int n )

The function should return the value true if n is a prime and false otherwise.Remember that a number is prime if is isn’t evenly divisible by anything except for 1 and itself. You can figure this out by using a for loop inside the function.Make the for loop run through all the numbers from 2 up to n. Inside the loop, use an if statement that determines if n is evenly divisible by your loop control variable.If you find any number which divides it evenly, you can go ahead and return false from the function without finishing the loop.If the loop finishes and doesn’t find any numbers which divide it, then return true from the function.After you finish writing the function write a main() that contains another for loop. Have it print out all the numbers from 2 to 20, and mark each prime number with a ”<”.Sample Output

public class FindingPrimeNumbers
{
    public static void main( String[] args )
    {
        for ( int i = 2; i <= 20; i++ )
        {
            if ( isPrime(i) )
                System.out.println(i + " <");
            else
                System.out.println(i);
        }
    }

    public static boolean isPrime( int n )
    {
        for ( int i = 2; i < n; i++ )
        {
            if ( n % i == 0 )
                return false;
        }

        return true;
    }
}

Persiapan Belajar

Materi

Task

Programming by Doing

Compiler

Functions Part 2

110. Keychains for Sale, real ultimate power - Link

111. Calling Functions from Other Files - Link

112. Evenness Function - Link

113. Finding Prime Numbers - Link

Persiapan Belajar

Materi

Task

Programming by Doing

Compiler

​110. Keychains for Sale, real ultimate power - Link

​111. Calling Functions from Other Files - Link

​112. Evenness Function - Link

​113. Finding Prime Numbers - Link

110. Keychains for Sale, real ultimate power - Link

111. Calling Functions from Other Files - Link

112. Evenness Function - Link

113. Finding Prime Numbers - Link