LOOPS - Introduction to Java Programming: Comprehensive Version - page 164

5.2.3 Case Study: Multiple Subtraction Quiz
The Math subtraction learning tool program in Listing 3.3, SubtractionQuiz.java, generates just
one question for each run. You can use a loop to generate questions repeatedly. How do you
write the code to generate five questions? Follow the loop design strategy. First identify the
statements that need to be repeated. These are the statements for obtaining two random numbers,
prompting the user with a subtraction question, and grading the question. Second, wrap the state-
ments in a loop. Third, add a loop control variable and the loop-continuation-condition
to execute the loop five times.
Listing 5.4 gives a program that generates five questions and, after a student answers all
five, reports the number of correct answers. The program also displays the time spent on the
test and lists all the questions.

VideoNote
Multiple subtraction quiz

L ISTING 5.4

SubtractionQuizLoop.java
1 import java.util.Scanner;
2
3 public class SubtractionQuizLoop {
4 public static void main(String[] args) {
5 final int NUMBER_OF_QUESTIONS = 5 ; // Number of questions
6 int correctCount = 0 ; // Count the number of correct answers
7 int count = 0 ; // Count the number of questions
8 long startTime = System.currentTimeMillis();
9 String output = " " ; // output string is initially empty
10 Scanner input = new Scanner(System.in);
11
12

get start time

while (count < NUMBER_OF_QUESTIONS) {

loop

13 // 1. Generate two random single-digit integers

14 int number1 = ( int )(Math.random() * 10 );

15 int number2 = ( int )(Math.random() * 10 );

16
17 // 2. If number1 < number2, swap number1 with number2
18 if (number1 < number2) {
19 int temp = number1;
20 number1 = number2;
21 number2 = temp;
22 }
23
24 // 3. Prompt the student to answer "What is number1 - number2?"
25 System.out.print(
26

display a question

"What is " + number1 + " - " + number2 + "? " );

27 int answer = input.nextInt();

28
29 // 4. Grade the answer and display the result
30 if (number1 - number2 == answer) {
31 System.out.println( "You are correct!" );
32 correctCount++; // Increase the correct answer count
33 }
34 else
35 System.out.println( "Your answer is wrong.\n" + number1
36 + " - " + number2 + " should be " + (number1 - number2));
37
38 // Increase the question count
39 count++;
40
41 output += "\n" + number1 + "-" + number2 + "=" + answer +
42 ((number1 - number2 == answer) ? " correct" : " wrong" );

grade an answer

increase correct count

increase control variable

prepare output