Add Ex 21.15

Author: jsquared21

Exercise_21/Exercise_21_15/Exercise_21_15.class

@@ -0,0 +1,35 @@
+/*********************************************************************************
+* (Addition quiz) Rewrite Programming Exercise 11.16 to store the answers in a   *
+* set rather than a list.                                                        *
+*********************************************************************************/
+import java.util.*;
+
+public class Exercise_21_15 {
+	public static void main(String[] args) {
+		int number1 = (int)(Math.random() * 10);
+		int number2 = (int)(Math.random() * 10);
+
+		// Create a Scanner
+		Scanner input = new Scanner(System.in);
+
+		// Create an set
+		Set<Integer> answers = new HashSet<>();
+
+		System.out.print(
+			"What is " + number1 + " + " + number2 + "? ");
+		int answer = input.nextInt();
+
+		while (number1 + number2 != answer) {
+			if (answers.contains(answer))
+				System.out.println("You already entered " + answer);
+			else {
+				System.out.print("Wrong answer. Try again. What is "
+					+ number1 + " + " + number2 + "? ");
+				answers.add(answer);
+			}
+			answer = input.nextInt();
+		}
+
+		System.out.println("You got it!");
+	}
+}