Problem: An Improved Math Learning Tool
Suppose you want to develop a program for a first-grader to
practice subtraction. The program randomly generates two single-digit integers,
number1 and number2, with number1 > = number2 and displays to the
student a question such as “What is 9-2? ” After the student enters the answer,
the program displays a message indicating whether it is correct. The previous
programs generate random numbers using System.currentTimeMillis(). A better approach is to use the random() method in the Math class.
Invoking this method returns a random double value d such 0.0 <= d <1.0 that So, (int)(Math.random()
* 10) returns a random single-digit integer (i.e., a
number between 0 and 9). The program may work as follows:
■ Generate two single-digit integers into number1 and number2.
■ If number1 < number2, swap number1 with number2.
■ Prompt the student to answer “What is number1 – number2?”
■ Check the student’s answer and display whether the answer is
correct.
File name : SubtractionQuiz.java
import java.util.Scanner;
public class SubtractionQuiz {
public static
void main(String[] args) {
// 1.
Generate two random single-digit integers
int number1
= (int)(Math.random() * 10);
int number2
= (int)(Math.random() * 10);
// 2. If
number1 < number2, swap number1 with number2
if (number1
< number2) {
int temp =
number1;
number1 =
number2;
number2 =
temp;
}
// 3. Prompt
the student to answer “what is number1 – number2?”
System.out.print
("What
is " + number1 + " - " + number2 + "? ");
Scanner
input = new Scanner(System.in);
int answer =
input.nextInt();
// 4. Grade
the answer and display the result
if (number1
- number2 == answer)
System.out.println("You are correct!");
else
System.out.println("Your answer is wrong.\n" + number1 +
" - "
+
number2 + " should be " + (number1 - number2));
}
}
