Java Scanner input validation causing loop to end early

Question

I am filling a Double Array with a for-loop, the loop runs for how many laps the user enters on line 4. However, as I demonstrate in my picture included:

I enter 3 laps and the question prompts 3 times however my data validation eats one of the inputs I am looking for.

How do I fix this? I feel like its something very simple.

import java.util.Scanner;
public class JK_FINALPRAC1 {

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        System.out.println("Time-Trial Statistics Program\n");
        System.out.println("This program will ask you to input split-times for each lap or length of a race. The ");
        System.out.println("program will then calculate some basic statistics from the split-times.\n");

        System.out.print("Enter the number of laps or lengths in the race: ");
        int arraySize = sc.nextInt();
        Double[] lapArray = new Double[arraySize];
        System.out.println("Now input the elapsed time (split time) in seconds for each lap/length of the race.");
        int index = 1;
        double currentNum = 0.0;
        for(int i=0;i<arraySize;i++){
            System.out.print("Time for lap or length #" + index + ": ");
            currentNum = sc.nextDouble();
            if(currentNum > 0 && currentNum < 61){
            lapArray[i] = currentNum;
            index++;
            }else if(currentNum<0 || currentNum >60){
            System.out.println("Invalid input! Time must be between 0 and 60.");
            }
        }

    }

VaibS · Accepted Answer · 2021-04-20 06:14:18Z

1

        double currentNum = 0.0;
        while (index < arraySize) {
            System.out.print("Time for lap or length #" + (index + 1) + ": ");
            currentNum = sc.nextDouble();
            if (currentNum > 0 && currentNum < 61) {
                lapArray[index] = currentNum;
                index++;
            } else if (currentNum < 0 || currentNum > 60) {
                System.out.println("Invalid input! Time must be between 0 and 60.");
            }
        }

Since you're running for-loop, i is getting incremented every time (even if your validation fails).

answered Apr 20, 2021 at 6:14

VaibS

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Comments

DynoZ · Accepted Answer · 2021-04-20 06:14:54Z

1

It's very simple: in order to be sure you have inserted a double without eat a lap, put your scanner input line inside a while-loop

 do{
    double x = scanner.nextDouble(); 
 }while(x < 0 || x > 60);

This will not afford for-loop increasing counter, unless the condition of do-while is false.

In order to print validation, too:

 double x = scanner.nextLine();
 while( x < 0 || x > 60){
      //print message
      //scanner again
 }

edited Apr 20, 2021 at 6:14

answered Apr 20, 2021 at 6:03

DynoZ

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2 Comments

JK3 Over a year ago

How do i still have my Validation rules printed (ex. Invalid input! Time must be between 0 and 60.) if they do go out of bounds?

DynoZ Over a year ago

You mean that you wanna print validation rule every time double insrted is wrong? Then I suggest you to use a while-loop and not a do-while (this in order to not print your validation also the first input). You just need to make the input, check it in a while, and if it is wrong, print your validation rule and remake input. I am gonna edit my post

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