CS 1063 -- Review for Exam 2, Answers

CS 1063 Intro. to Programming
Topics and Review Questions for
Exam 2, Fall 2005
Selected Answers

Sample Questions: I will pick simple questions about many of the topics from the web pages and from class. Often it will involve giving you some code and asking you to explain, modify, or complete the code.

How do you translate a mathematical equation, such as the quadratic formula, into Java?

Given and integer, such as int n = 47;, how do you use the / and % operators to pick off the ten's digit and the unit's digit?

import java.util.Scanner;

public class Digits {

   public static void main(String[] args) {
      Scanner in = new Scanner(System.in);
      System.out.print("Type an integer ---> ");
      int digits = in.nextInt();
      int tensDigit = digits / 10;
      int unitsDigit = digits % 10;
      System.out.println("Number: " + digits +
         ", Tens: "  + tensDigit + 
         ", Units: " + unitsDigit);
   }
}

Output of three runs:
Type an integer ---> 47
Number: 47, Tens: 4, Units: 7

Type an integer ---> 8
Number: 8, Tens: 0, Units: 8

Type an integer ---> 92
Number: 92, Tens: 9, Units: 2

Starting with two integers, say int a = 47; and int b = 89;, how can you use an extra integer location, say int temp; and three assignments to interchange the values in a and b?

As in the previous example, also use an if statement to ensure that, no matter what the starting values of a and b, after the statement the two values are the same, but possibly interchanged so that a <= b is always true.

public class Testit {

   public static void main(String[] args) {
      int a = 89;
      int b = 47;
      System.out.println("a: " + a + ", b: " + b);
      if (a > b) {
         int temp = a;
         a = b;
         b = temp;
      }
      System.out.println("a: " + a + ", b: " + b);
   }
}

Output of a run:
a: 89, b: 47
a: 47, b: 89

Give several different ways to increase the value of an integer variable, say int x; by one.
Start with two strings, say s1 and s2. Use an if-else statement and the equals method to check if the strings are equal, and to print either EQUAL or print NOT EQUAL. (You must not use either of the operators == or !=.)

Start with two strings, say s1 and s2. Use an extended if-else statement and the compareTo method to do a dictionary order comparison of the two strings. Your statement should print one of the three messages: FIRST-BEFORE-SECOND, FIRST-AFTER-SECOND, or FIRST-EQUALS-SECOND.

public class Testit2 {

   public static void main(String[] args) {
      String s1 = "Stephen";
      String s2 = "Stephany";
      if (s1.compareTo(s2) < 0)      System.out.println("FIRST-BEFORE-SECOND");
      else if (s1.compareTo(s2) > 0) System.out.println("FIRST-AFTER-SECOND");
      else                           System.out.println("FIRST-EQUALS-SECOND");
   }
}

Output of a run:
FIRST-AFTER-SECOND

Work out the examples in the Activity 1 of the Week 10 lecture:

Assign theMin to be the smaller of x and y
Write an if statement that assigns 100 to x when y is equal to 0.
Write an if-else statement that assigns 0 to x when y is equal to 10. Otherwise it should assign 1 to x.
Write an if statement that sets the variable hours to 10 when the boolean variable minumum is equal to true

Calculate wages as hoursWorked times hourlyRate with time and a half for overtime (hours over 40)

public class Wages {

   public static void main(String[] args) {
       double hoursWorked = 50.0;
       double hourlyRate = 10.0;
       double wages;
       if (hoursWorked <= 40.0) {
          wages = hoursWorked*hourlyRate;
       }
       else {  // hoursWorked > 40.0
          wages = hourlyRate*40.0 +
             (hoursWorked - 40.0)*hourlyRate*1.5;
       }
       System.out.println("Hours worked: " + hoursWorked +
          ", Hourly rate: " + hourlyRate +
          ", Wages: " + wages);
   }
}

Output of a run:
Hours worked: 50.0, Hourly rate: 10.0, Wages: 550.0

Here's a slightly different method:

public class Wages2 {

   public static void main(String[] args) {
       double hoursWorked = 50.0;
       double hourlyRate = 10.0;
       double wages;
       // first apply normal rate to all hours
       wages = hoursWorked*hourlyRate;
       // now add in extra half rate for hours > 40
       if (hoursWorked > 40.0) {
          wages = wages + (hoursWorked - 40.0)*hourlyRate*0.5;
       }
       System.out.println("Hours worked: " + hoursWorked +
          ", Hourly rate: " + hourlyRate +
          ", Wages: " + wages);
   }
}

Output of a run:
Hours worked: 50.0, Hourly rate: 10.0, Wages: 550.0

Work out the first three examples in the Activity 2 of the Week 11 lecture:
- Write an if statement that prints the message "The number is valid" if the variable grade is within the range 0 through 100 inclusive.
- Write an if statement that prints the message "The number is valid" if the variable temperture is within the range -50 through 150 inclusive.
- Write an if statement that prints the message "The number is not valid" if the variable hours is outside the range 0 through 80 inclusive.
Given a table such as the one given in the The Commission class, write an if-else statement to set the value correctly. (Three answers given.)

Given and integer number of points on and exam in the variable int points;, print the proper grade using the table below:

points	Grade
greater than 100	A+
90 to 100 inclusive	A
80 to 89 inclusive	B
70 to 79 inclusive	C
60 to 79 inclusive	D
0 to 59 inclusive	F
less than 0	Invalid

import java.util.Scanner;

public class Grades {

   public static void main(String[] args) {
      Scanner in = new Scanner(System.in);
      System.out.print("Type an integer ---> ");
      int points = in.nextInt();
      String grade = "";
      if (points > 100) grade = "A+";
      else if (points >= 90 && points <= 100) grade = "A";
      else if (points >= 80 && points <   90) grade = "B";
      else if (points >= 70 && points <   80) grade = "C";
      else if (points >= 60 && points <   70) grade = "D";
      else if (points >=  0 && points <   60) grade = "F";
      else if (points <   0) grade = "Invalid";
      System.out.println("Points: " + points +
         ", Grade: "  + grade);
   }
}

Output of multiple runs:
Type an integer ---> 101
Points: 101, Grade: A+

Type an integer ---> 100
Points: 100, Grade: A

Type an integer ---> 90
Points: 90, Grade: A

Type an integer ---> 89
Points: 89, Grade: B

Type an integer ---> 80
Points: 80, Grade: B

Type an integer ---> 60
Points: 60, Grade: D

Type an integer ---> 59
Points: 59, Grade: F

Type an integer ---> 0
Points: 0, Grade: F

Type an integer ---> -1
Points: -1, Grade: Invalid

I plan to have a question involving a class and a test class (with a main function). I will supply a description and part of the code. You will have to fill in various missing parts. For example, I may ask you to supply constructor(s) or method(s) in the class, and to use these in the main function. At least somewhere you will need to use assignments, arithmetic operators, comparison operators, and if-else statements.
You have prepared for this question by having done the labs. The question will be similar to these labs, but simpler. You can also prepare by looking over or working out the two extra review classes in the Week 12 Review: the Triangle class, and the RomanNumeral class. (Note that the switch statement in the answer to the question about the RomanNumeral class in not required. It can easily be done with an extended if-else statement.)

CS 1063 Intro. to Programming Topics and Review Questions forExam 2, Fall 2005 Selected Answers

CS 1063 Intro. to Programming
Topics and Review Questions for
Exam 2, Fall 2005
Selected Answers