When the user input an invalid value, like a String or character, the program should ignore it and show the previous question again. So far I can only make the program quit when it catch invalid input.
Valid inputs are int
and "q", which user decided to quit.
public static void partB() {
int score = 0;
int correct = 0;
int done = 0;
Scanner scan = new Scanner(System.in);
try {
while (true) {
int num1 = (int) (Math.random() * 20);
int num2 = (int) ((Math.random() * 20) + 1);
System.out.printf("%d %% %d = ?\n", num1, num2);
if (scan.hasNext("q")) break;
if (scan.nextInt() == (num1 % num2)) {
score += 20;
done += 1;
correct += 1;
System.out.println("Correct answer,current score :" + score
+ ",performance: "
+ correct + "/" + done);
} else {
done += 1;
System.out.println("Incorrect answer, Current score:" +
score
+ ", performance: " + correct + "/" + done);
}
}
} catch (InputMismatchException e) {
System.out.println("invalid input"); //but this terminate program
}
System.out.println("Finish");
}
And the code is supposed to run like this:
18 % 12 = ?
6
Correct answer, Current score: 20, performance: 1/1
14 % 16 = ?
a
Invalid input
14 % 16 = ?
14
Correct answer, Current score: 40, performance: 2/2
20 % 4 = ?
q
Finish.
You need to move the try-catch
inside the while
block. Also when there is a InputMismatchException
you have to finish reading the line (because you used Scanner#nextInt
instead of Scanner#nextLine
) and set a variable (repeatValue
) to true
. With this variable you can decide whether you need to generate new values or use the previous ones.
See it running here:
public static void main(String[] args) {
int score = 0;
int correct = 0;
int done = 0;
Scanner scan = new Scanner(System.in);
boolean repeatValue = false;
int num1 = 0; // put values outside while in order to re-use them when we need to repeat the same question
int num2 = 0;
while (true) {
try {
// if the user input was incorrect (repeatValue = true), use old the previous values for num1 and num2
num1 = repeatValue ? num1 : (int) (Math.random() * 20);
num2 = repeatValue ? num2 : (int) ((Math.random() * 20) + 1);
System.out.printf("%d %% %d = ?\n", num1, num2);
repeatValue = false; // restore flag state
if (scan.hasNext("q"))
break;
if (scan.nextInt() == (num1 % num2)) {
score += 20;
done += 1;
correct += 1;
System.out.println(
"Correct answer,current score :" + score + ",performance: " + correct + "/" + done);
} else {
done += 1;
System.out.println(
"Incorrect answer, Current score:" + score + ", performance: " + correct + "/" + done);
}
} catch (InputMismatchException e) {
System.out.println("invalid input");
scan.next();
repeatValue = true; // flag set to use the same values as before
}
}
System.out.println("Finish");
}