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  #1  
Old 14-11-2009
Member
 
Join Date: Nov 2009
Posts: 583
Java Loop help

Hi
I have to complete an assignment, for which I am trying to write a program. I have posted my code below and all the instruction are in the comments.
Code:
public class MathOperationsTester
{
    public static void main(String[] args)
    {
        Scanner in = new Scanner(System.in);
        System.out.println( "TESTING sumOfIntegers"  );
        // STEP 3:  The next two statements request the user to enter the value of n and then reads in their response as an int using the
        //      nextInt method of the Scanner class.
        //      The problem with this is that if the user enters something other than an int, we will have a runtime exception.
        //      After requesting the user enters n (first of the next two statements), write a while loop that repeats as long as the user
        //     enters something other than an int (recall that the hasNextInt method of the Scanner class will return true if the user
        //    enters an int and false otherwise.  And recall that ! is Java's not operator.  Inside the loop, you'll want to remove whatever they
        // did enter with a call to the next method of the Scanner class.  And you'll want to give them an error message indicating that they should try again.
        //  This loop should be immediately prior to the call to the nextInt method which has been done for you.
        System.out.println( "Enter n:");
        // Your loop from Step 3 will go here.
   while( !hasNextInt())
     System.out.println("Please enter a valid integer");
        int n = in.nextInt();
        int sum = MathOperations.sumOfIntegers(n);
        System.out.println("Sum of first " + n + " integers is " + sum);
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  #2  
Old 14-11-2009
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Join Date: May 2008
Posts: 2,293
Re: Java Loop help

It seems hasNextInt() is a test to see if the next thing in the scanner is an int, and the single body of this while loop to print out please enter a valid integer repeats forever right ?
I suggest you for the loop to
1) display a prompt
2) try to read any input from the user
3) try to see if the input we read is an integer, if so we are done.
Code:
public class ScannerReadInt {
  public static void main(String[] args) {
       Scanner sc= new Scanner(System.in); 
     int intv = 0;
     boolean validInput = false;
     while (!(validInput)) {
       System.out.print("Please enter a number: ");
       String str = scanner.next();
       try {
         intv = Integer.parseInt(str);
         validInput = true;
         // or, we could break here too to get out of the loop.
       }
       catch (NumberFormatException ex) {
         // the thing entered is not a valid integer
         System.out.println("Invalid number (" + str + ")");
       }
     }
     System.out.println("you entered: " + intv);
  }
}
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  #3  
Old 14-11-2009
Member
 
Join Date: Nov 2009
Posts: 583
Re: Java Loop help

Thanks for the help
That looks really good and I appreciate you work, but I think the code is bit of complex for this assignment. I tried it and implemented it, but I came to some errors. I think I am not familiar with the try and catch ideas of java yet. Anything more easy would do for me, that would be simpler for my assignment. But I am going to keep messing around this code and codes like these so I can learn java quickly. Thanks for you help again.
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