Check user input and for loop

Question

I encountered a problem with my for loop.

My objective is to

Check that integers are entered instead of strings by user.
Loop it 6 times, each time prompting the user for input.

With my current code, I am getting this output:

Enter integer: 
a
invalid input
Enter integer: 
invalid input
Enter integer: 
invalid input
Enter integer: 
invalid input
Enter integer: 
invalid input
Enter integer: 
invalid input
BUILD SUCCESSFUL (total time: 3 seconds)

I am able to check the user input for integer. However, my for loop doesn't seem to be working correctly. May I request assistance in this?

Below is my code:

String a = "";
int count;

for (count = 0; count < 6; count++) {
    System.out.println("Enter integer: ");

    if (keyboard.hasNextInt()) {  
        System.out.println(a + "is correct integer"); 
    }
    else {
        System.out.println("invalid input");
    }
}

Elliott Frisch · Accepted Answer · 2015-01-05 12:04:49Z

4

You aren't consuming any of the user input and a should be an int if you're going to read int(s). I think you wanted something like

for (int count = 0; count < 6; count++) {
    System.out.println("Enter integer: ");
    if (keyboard.hasNextInt()) {
        int a = keyboard.nextInt();
        System.out.printf("%d is an integer%n", a);
    } else {
        System.out.println("invalid input " + keyboard.nextLine());
    }
}

answered Jan 5, 2015 at 12:04

Elliott Frisch

202k20 gold badges166 silver badges265 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

Tom Over a year ago

I guess you should change nextLine to next, because nextLine would first read the remainin line feed and on the next iteration the invalid input. This "wastes" one interation.

gknicker · Accepted Answer · 2015-01-05 12:10:15Z

2

You must consume the keyboard input, else it will still be there in subsequent loop iterations.

if(keyboard.hasNextInt())
{
  // consume the input by calling nextInt()
  System.out.println(keyboard.nextInt() + " is correct integer"); 
}
else
{
  // consume the input by calling next()
  System.out.println("invalid input " + keyboard.next());
}

answered Jan 5, 2015 at 12:10

gknicker

5,5982 gold badges29 silver badges44 bronze badges

Comments

Jens · Accepted Answer · 2015-01-05 12:18:24Z

2

Try this:

it consumes the wrong line and as you again.

                String a = "";
    int count;
    Scanner keyboard = new Scanner(System.in);
    for (count = 0; count < 6; count++) {
        System.out.println("Enter integer: ");

        if (keyboard.hasNextInt()) {
            a = String.valueOf(keyboard.nextInt());
            System.out.println(a + "is correct integer");
        } else {
            System.out.println("invalid input");
            keyboard.nextLine();
        }
    }

edited Jan 5, 2015 at 12:18

answered Jan 5, 2015 at 12:04

Jens

69.6k15 gold badges107 silver badges133 bronze badges

3 Comments

gymcode Over a year ago

Thank you Jens. I am now able to prompt user for another input if he enters a Char. However, when he enters an Int, the loop still malfunctioned. It gives the same output of not prompting the user for another input.

Jens Over a year ago

@RUiHAO: I have changed my answer. Please try again.

Tom Over a year ago

I guess you should change nextLine to next, because nextLine would first read the remainin line feed and on the next iteration the invalid input. This "wastes" one interation.

Community · Accepted Answer · 2017-05-23 10:26:09Z

1

Your code needs following changes:

Assign String a with input value:

if (keyboard.hasNextInt()) {
    a = keyboard.next();
    System.out.println(a + "is correct integer");
} else {
    a = keyboard.next();
    System.out.println("invalid input");
}

initialize keyboard variable properly:

Scanner keyboard = new Scanner(System.in);

This question might be helpful Java: using hasNextInt with do-while loop, it ignores integer inputs at even times.

edited May 23, 2017 at 10:26

CommunityBot

11 silver badge

answered Jan 5, 2015 at 12:12

100rabh

1369 bronze badges

2 Comments

gymcode Over a year ago

This worked for me. I am very puzzled. In the other codes, I will meet an InputMismatchException when I enter an incorrect input after the previous correct input (entering wrong input after a correct input). However, in this code, the error did not appear. May I know if anyone know the reason why?

100rabh Over a year ago

@RUiHAO You haven't mentioned 'Other codes' but In my opinion you were getting InputMismatchException because you were consuming 'incorrect input'(a string input) with keyboard.nextInt(); Now in my code above, we are consuming every input with keyboard.next(); which works fine with int/string inputs. Please check following links for more details:: docs.oracle.com/javase/7/docs/api/java/util/Scanner.html docs.oracle.com/javase/7/docs/api/java/util/…

JustStarted · Accepted Answer · 2015-01-05 12:25:47Z

0

    for (int i = 0; i < 6; i++){
        Scanner input = new Scanner(System.in);
        System.out.println("Enter integer:");
        char value = input.nextLine().charAt(0);
        if(Character.isDigit(value)){
            System.out.println(value + " is correct integer"); 
        }else{
            System.out.println(value + " invalid input");
        }

    }

answered Jan 5, 2015 at 12:25

JustStarted

3191 gold badge5 silver badges15 bronze badges

1 Comment

Tom Over a year ago

"-1" is not a valid integer? That's sad :(.

Dilip · Accepted Answer · 2015-01-05 12:09:45Z

-3

You need to Scan the Value from system therefore use Import scanner

**

USE this code

**

Scanner s = new Scanner(System.in);
        int i;
        String a = "";
        int count;

        for (count = 0; count<6; count++)
                {
            System.out.println("Enter integer: ");

            if(s.hasNextInt()) 
                        {  
                        System.out.println(a + "is correct integer"); 
                        }
                        else
                        {
                        System.out.println("invalid input");
                        }
                }

answered Jan 5, 2015 at 12:09

Dilip

2,7501 gold badge23 silver badges27 bronze badges

1 Comment

gknicker Over a year ago

The keyboard variable in his code example is already a Scanner.

Collectives™ on Stack Overflow

Check user input and for loop

6 Answers 6

1 Comment

Comments

3 Comments

2 Comments

1 Comment

You need to Scan the Value from system therefore use Import scanner

USE this code

1 Comment

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

6 Answers 6

1 Comment

Comments

3 Comments

2 Comments

1 Comment

You need to Scan the Value from system therefore use Import scanner

USE this code

1 Comment

Your Answer

Sign up or log in

Post as a guest

Linked

Related