Store the numbers in a array in Java

[shashankraj1231]

I am trying to write a Java program in which we would take input from the user until
the user enters -1. The input would be integers and has to be stored in a integer array.

I am a newbie in Java and i am trying to self study here. Please tell me what am i doing wrong. It would be of great help.

class storearray{
    public static void main(String args[]) throws IOException
    {
        BufferedReader dis= new BufferedReader(new InputStreamReader(System.in));
        int arr[]= new int[10];
        System.out.println("Enter elements of an array");
        System.out.println("Enter -1 to quit");
        int i=0;
        String data;
        System.out.flush();
        for(i=0;arr[i]!= -1; i++){
                data= dis.readLine();
                try{
                arr[i]= Integer.parseInt(data);
                } catch(NumberFormatException e)
                {
                    System.out.println("Invalid FOrmat");
                    //arr[i]=0;
                }
              System.out.println("The values of the array are :"+" "+arr[i]+" "+"i= "+i);
            } 
            for(int x:arr)
                System.out.println(x);
        }
 
    }
 

[Dheeraj Joshi]

Your for loop need some changes

for(i=0;arr[i]!= -1; i++)
 

Your code runs till arr[i] != -1
Your program will throw array index out of bound exception. Since you defined array of size 10 and your for loop do not terminate. User is able to add 11th elements.

Your for loop should look like

for(int iCount=0;iCount<10;iCount++)
{
        //Logic here
}
 

Please catch a generic exception and see what exception it will throw.

Regards
Dheeraj Joshi

[jkmyoung]

for(i=0;arr[i]!= -1; i++)
The problem is that in a for loop, the increment runs before the conditional check.
So let's say the first number is -1. You put -1 in arr[0].
Then i++ -> i = 1
The for loop checks, is arr[1] != -1? No.

But you meant to check arr[0], not arr[1].

You might want to have a different check INSIDE the for loop, eg:
if number entered was -1, break out of the for loop.

[shashankraj1231]

@jkmyoung
Thank you very much for that explanation, I understand the For-Loop much better now. I was not aware that the the increment runs before the conditional check.
I corrected the program by adding
if (arr[i]== -1)
break;

and it works like magic now.

Regards,
Shashank.

[shashankraj1231]

@dheerajjoshim
Thank you for the explanation of the exception. That gave me a clear understanding of how it works.

Regards,
Shashank.