Chapter 5: Conditionals and Loops

Lab Exercises

 

Topics                                                 Lab Exercises

Boolean expressions                                           PreLab Exercises  (in-class)               

The if statement                                                   Computing a Raise   (in-class)

The switch statement                                          A Charge Account Statement (submit)                           

Activities at Lake LazyDays (submit)

Rock, Paper, Scissors (extra credit)

 

 

 


Prelab Exercises

Sections 5.1-5.3

 

1.     Rewrite each condition below in valid Java syntax (give a boolean expression):

a.     x > y > z

b.     x and y are both less than 0

c.     neither x nor y is less than 0

d.     x is equal to y but not equal to z

 

2.     Suppose gpa is a variable containing the grade point average of a student. Suppose the goal of a program is to let a student know if he/she made the Dean's list (the gpa must be 3.5 or above). Write an if... else... statement that prints out the appropriate message (either "Congratulations—you made the Dean's List" or "Sorry you didn't make the Dean's List").

 

3.     Complete the following program to determine the raise and new salary for an employee by adding if ... else statements to compute the raise. The input to the program includes the current annual salary for the employee and a number indicating the performance rating (1=excellent, 2=good, and 3=poor). An employee with a rating of 1 will receive a 6% raise, an employee with a rating of 2 will receive a 4% raise, and one with a rating of 3 will receive a 1.5% raise.

 

// ***************************************************************

//   Salary.java

//   Computes the raise and new salary for an employee

// ***************************************************************

import java.util.Scanner;

 

public class Salary

{

   public static void main (String[] args)

   {

      double currentSalary;  // current annual salary

      double rating;         // performance rating

      double raise;          // dollar amount of the raise

 

      Scanner scan = new Scanner(System.in);

 

      // Get the current salary and performance rating

      System.out.print ("Enter the current salary: ");

      currentSalary = scan.nextDouble();

      System.out.print ("Enter the performance rating: ");

      rating = scan.nextDouble();

 

      // Compute the raise -- Use if ... else ...

 

      // Print the results

      System.out.println ("Amount of your raise: $" + raise);

      System.out.println ("Your new salary: $" + currentSalary + raise);

   }

}


Computing A Raise

 

File Salary.java contains most of a program that takes as input an employee's salary and a rating of the employee's performance and computes the raise for the employee. This is similar to question #3 in the pre-lab, except that the performance rating here is being entered as a String—the three possible ratings are "Excellent", "Good", and "Poor". As in the pre-lab, an employee who is rated excellent will receive a 6% raise, one rated good will receive a 4% raise, and one rated poor will receive a 1.5% raise.

 

Add the if... else... statements to program Salary to make it run as described above. Note that you will have to use the equals method of the String class (not the relational operator ==) to compare two strings (see Section 5.3, Comparing Data).

 

 

 

// ***************************************************************

//   Salary.java

//

//   Computes the amount of a raise and the new

//   salary for an employee.  The current salary

//   and a performance rating (a String: "Excellent",

//   "Good" or "Poor") are input.

// ***************************************************************

 

import java.util.Scanner;

import java.text.NumberFormat;

 

public class Salary

{

   public static void main (String[] args)

   {

       double currentSalary;  // employee's current  salary

       double raise;          // amount of the raise

       double newSalary;      // new salary for the employee

       String rating;         // performance rating

 

       Scanner scan = new Scanner(System.in);

 

       System.out.print ("Enter the current salary: ");

       currentSalary = scan.nextDouble();

       System.out.print ("Enter the performance rating (Excellent, Good, or Poor): ");

       rating = scan.next();

 

       // Compute the raise using if ...

 

       newSalary = currentSalary + raise;

 

       // Print the results

       NumberFormat money = NumberFormat.getCurrencyInstance();

       System.out.println();

       System.out.println("Current Salary:       " + money.format(currentSalary));

       System.out.println("Amount of your raise: " + money.format(raise));

       System.out.println("Your new salary:      " + money.format(newSalary));

       System.out.println();

    }

}


A Charge Account Statement

 

Write a program to prepare the monthly charge account statement for a customer of CS CARD International, a credit card company. The program should take as input the previous balance on the account and the total amount of additional charges during the month. The program should then compute the interest for the month, the total new balance (the previous balance plus additional charges plus interest), and the minimum payment due. Assume the interest is 0 if the previous balance was 0 but if the previous balance was greater than 0 the interest is 2% of the total owed (previous balance plus additional charges). Assume the minimum payment is as follows:

 

         new balance          for a new balance less than $50

           $50.00             for a new balance between $50 and $300 (inclusive)

    20% of the new balance    for a new balance over $300

 

So if the new balance is $38.00 then the person must pay the whole $38.00; if the balance is $128 then the person must pay $50; if the balance is $350 the minimum payment is $70 (20% of 350). The program should print the charge account statement in the format below. Print the actual dollar amounts in each place using currency format from the NumberFormat class—see Listing 3.4 of the text for an example that uses this class.

 

 

         CS CARD International Statement

         ===============================

 

         Previous Balance:      $

         Additional Charges:    $

         Interest:              $

 

         New Balance:           $

 

         Minimum Payment:       $


Activities at Lake LazyDays

 

As activity directory at Lake LazyDays Resort, it is your job to suggest appropriate activities to guests based on the weather:

 

  temp >= 80:       swimming

  60 <= temp < 80:  tennis

  40 <= temp < 60:  golf

  temp < 40:        skiing

 

1.     Write a program that prompts the user for a temperature, then prints out the activity appropriate for that temperature. Use a cascading if, and be sure that your conditions are no more complex than necessary.

 

2.    Modify your program so that if the temperature is greater than 95 or less than 20, it prints "Visit our shops!". (Hint: Use a boolean operator in your condition.) For other temperatures print the activity as before.


Rock, Paper, Scissors

 

Program Rock.java contains a skeleton for the game Rock, Paper, Scissors. Open it and save it to your directory. Add statements to the program as indicated by the comments so that the program asks the user to enter a play, generates a random play for the computer, compares them and announces the winner (and why). For example, one run of your program might look like this:

 

$ java Rock

Enter your play: R, P, or S

r

Computer play is S

Rock crushes scissors, you win!

 

Note that the user should be able to enter either upper or lower case r, p, and s. The user's play is stored as a string to make it easy to convert whatever is entered to upper case. Use a switch statement to convert the randomly generated integer for the computer's play to a string.

 

// ****************************************************************

//   Rock.java

//

//   Play Rock, Paper, Scissors with the user

//         

// ****************************************************************

import java.util.Scanner;

import java.util.Random;

 

public class Rock

{

    public static void main(String[] args)

    {

      String personPlay;    //User's play -- "R", "P", or "S"

      String computerPlay;  //Computer's play -- "R", "P", or "S"

      int computerInt;      //Randomly generated number used to determine

                            //computer's play

 

      Scanner scan = new Scanner(System.in);

      Random generator = new Random();

 

      //Get player's play -- note that this is stored as a string

      //Make player's play uppercase for ease of comparison

      //Generate computer's play (0,1,2)

      //Translate computer's randomly generated play to string

      switch (computerInt)

{

 

      }

 

      //Print computer's play

      //See who won.  Use nested ifs instead of &&.

      if (personPlay.equals(computerPlay)) 

          System.out.println("It's a tie!");

      else if (personPlay.equals("R"))

          if (computerPlay.equals("S"))

            System.out.println("Rock crushes scissors.  You win!!");

          else

 

            //...  Fill in rest of code

    }

}