Check loop if input are all integer

Question

I'm making simple program where the user inputs a class number of a student(cn) and the grade of that student(ngrade). I was trying to add an exception that checks if the input of the cn and ngrade are integers. If not the user will be informed that it is invalid and asks to re enter the details.

problem: i did use while loop to check the inputs throughout the loop. but i'm getting a infinite loop.

CODE:

import java.io.*;
import java.util.*;

public class trrying {

    public static void main(String[] args) {
        int ngrade;
        int cn;
        int A = 0, B = 0, C = 0, D = 0, E = 0;
        boolean test = false;
        Scanner sn = new Scanner(System.in);

        while (!test) {
            try {
                for (int i = 0; i <= 2; i++) {

                    System.out.println("Enter class number: ");
                    cn = sn.nextInt();
                    System.out.println("Enter numeric grade: ");
                    ngrade = sn.nextInt();
                    System.out.println("Letter Grade: ");

                    if (ngrade >= 90) {
                        A++;
                        System.out.println("A");
                    } else {
                        System.out.println("HELLO");
                    }

                    test = true;

                }
                test = false;
            } catch (Exception e) {
                System.out.println("ERROR! ");
                // System.out.println("Enter class number: ");

            }

        }
    }
}

Related: [Validating input using java.util.Scanner](http://stackoverflow.com/questions/3059333/validating-input-using-java-util-scanner), [How to use Scanner to accept only valid int as input](http://stackoverflow.com/questions/2912817/how-to-use-scanner-to-accept-only-valid-int-as-input) — Pshemo, Feb 19 '17 at 13:43

Tim Biegeleisen · Accepted Answer · 2017-02-19T13:45:14.943

-2

One option to get the behavior you want would be to read in each input as a string, using Scanner#nextLine(), and then manually try to parse that input as an integer. If successful, accept that input and continue with your logic. If not successful, then catch the exception, and repeat the loop to get another user input.

for (int i=0; i <= 2; i++) {
    String line = "";
    while (true) {
        System.out.println("Enter class number: ");
        line = sn.nextLine();
        try {
            cn = Integer.parseInt(line);
            break;
        } catch(Exception e) {
            System.out.println("Enter class number as an integer only.");
        }
    }
    while (true) {
        System.out.println("Enter numeric grade: ");
        line = sn.nextLine();
        try {
             ngrade = Integer.parseInt(line);
             break;
        } catch(Exception e) {
            System.out.println("Enter numeric grade as an integer only.");
        }
    }

    System.out.println("Letter Grade: ");

    if (ngrade >= 90) {
        System.out.println("A");
    }        
    else {
         System.out.println("HELLO");
    }

    test = true;
}

edited Feb 19 '17 at 13:45

answered Feb 19 '17 at 13:43

Tim Biegeleisen

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Note: I began penning this answer before it was marked as duplicate. I will leave this answer here so the OP can see one way of solving this problem. – Tim Biegeleisen Feb 19 '17 at 13:43
Please consider adding explanatory text and making it a community wiki – Hovercraft Full Of Eels Feb 19 '17 at 13:44
When you edit the answer, you'll see a checkbox that does just this. It should be fairly easy to find. – Hovercraft Full Of Eels Feb 19 '17 at 13:48
Not the down-voter, but now down-votes won't affect you. – Hovercraft Full Of Eels Feb 19 '17 at 13:49

Check loop if input are all integer

1 Answers1