Styjun

I'm new to Java. I want to get loop input except when the user inputs 0 that terminates the program in Java. I know how to implement this in C++ (as shown below), but the Java code I wrote doesn't work.

C++:

while (cin >> n, n) 
 GraphAdjList G;
 CreateAdjListGraph(G, n);
 n = 0;

Java:

Scanner sc = new Scanner(System. in );
n = sc.nextInt();
while (n != 0) 
 Graph G = new Graph();
 G.CreateAdjListGraph(n);
 //G.print();
 n = sc.nextInt();

This is what I want. The program terminates only when the user inputs 0.

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nextInt() won't work for your case, If your input contains a non-integer word it throws InputMismatchException. You better use nextLine() and try to convert each word in to int with Integer.parseInt.

For example:

 int n = -1;
 Scanner sc = new Scanner(System.in);
 String line;

 while (n != 0)
 line = sc.nextLine();
 String[] splits = line.split(" ");
 System.out.println(Arrays.toString(splits));

 for (String split : splits) 
 try 
 n = Integer.parseInt(split);
 if (n == 0)
 break;
 //Graph G = new Graph();
 //G.CreateAdjListGraph(n);

 catch (NumberFormatException e) 
 // handling
 
 
 

This should work even if you give all inputs in the same line.

You should not use scan.nextInt() because in your sample program run you took some non-inetger values as input, so, in that case you code will fail.

Use scan.nextLine() this will take argument as String and not as Integer. Now you can change compare the results for your While loop.

Working Code:

import java.util.Scanner;
public class stackScanner

 public static void main(String[] args)
 
 Scanner scan = new Scanner(System.in);
 String input = scan.nextLine();

 // as you are now taking "String" from user so you have to compare it with "0" not 0
 while(!(input.equals("0"))) // while input is not 0
 
 // your code here
 input = scan.nextLine();
 
 

Note: I am using String.equals() and not == operator, reasons:

• As String.equals() always return boolean value it doesn't through any exception.


• We can use == operators for reference comparison (address comparison) and Stinrg.equals() method for content comparison. In simple words, == checks if both objects point to the same memory location whereas String.equals() evaluates to the comparison of values in the objects.

For more on String.equals()