import java.util.Scanner;

public class ArrayReview {
public static void main(String[] args){
    double[] doublesArray = createArray();
    printArray(doublesArray);
}

//"input method" create array of 10 doubles
public static double[] createArray() {
    Scanner userInput = new Scanner(System.in);
    double[] array = new double[10];
    System.out.println("Input 10 non-negative double numbers");
    for(int i = 0 ; i < array.length ; i  ) {
        //input validation
        while(!userInput.hasNextDouble()) {
            userInput.nextLine(); //throws away bad input
            System.out.println("Please input a valid double input");
        }
        if(userInput.hasNextDouble()) {
            array[i] = userInput.nextDouble();
        }
    }
    userInput.close();
    return array;
}

//print all values in an array of doubles
public static void printArray(double[] array) {
    for(int i = 0 ; i < array.length ; i  ) {
        System.out.print(array[i]   " ");
    }
}
}

I need to validate all the users input so that only non negative numbers are allowed into the array. Currently I was able to check if the user inputs a letter or special character but negative numbers are still able to go into the array.

I've tried using the "<" operand in the while statement to see if the userInput<0 but i'm getting an error if i do that. Would I be better off making a method that is solely dedicated to checking if its a negative or not or is there an easier way?

CodePudding user response：

You could extend the conditional expression of the while loop as follows:

for (int i = 0; i < array.length; i  ) {
    double value;
    while (!userInput.hasNextDouble() || (value = userInput.nextDouble()) < 0) {
        userInput.nextLine(); // throws away bad input
        System.out.println("Please enter a valid, non-negative double value");
    }
    
    array[i] = value;
}

CodePudding user response：

I tried using do-while instead of while. So I can access the input first.

public static double[] createArray() {
        Scanner userInput = new Scanner(System.in);
        double[] array = new double[10];
        double value;
        boolean isValid;
        System.out.println("Input 10 non-negative double numbers");

        for(int i = 0 ; i < array.length ; i  ) {
            //input validation
            do {
                value = userInput.hasNextDouble() ? userInput.nextDouble() : 0;
                if(value > 0) {
                    array[i] = value;
                    isValid = true;
                }else {
                    System.out.println("Please input a valid double input");
                    isValid = false;
                }
            }while(!isValid);

        }
        userInput.close();
        return array;
    }

CodePudding user response：

My approach would be, in the for loop of your createArray method to first get the input, then use while loop to see if input is less than 0 in which case you will prompt the user to input a positive number. This will loop until a positive input is received.

I have tested it on my end and seem to get the results you are looking for. Your createArray method should look something like this:

public static double[] createArray() {
    Scanner userInput = new Scanner(System.in);
    double[] array = new double[10];
    System.out.println("Input 10 non-negative double numbers");

    for(int i = 0 ; i < array.length ; i  ) {
        //input validation
        double input = userInput.nextDouble();
        while (input < 0) {
            System.out.println("Please input a positive number");
            input = userInput.nextDouble();
        }
        array[i] = input;
    }

    userInput.close();
    return array;
}