我得到了意外的整数值

Question

I am debugging a program to which the output should look like this, (though the indents are a bit wonky):

Enter a number you dislike 9

                       9
                      X9
               _________
                      81
               x12345679
               _________
Surprise           999999999
                   X1000
               _________
"No Surprise"?  999999999000

This is my code:

    import java.util.Scanner;
    import java.lang.Math;
    public class Prog76a

    {
     public static void main (String[] args)
   {   
  Scanner keyboard = new Scanner(System.in);

  //Prompting the user to enter a number
  System.out.print("Enter a number you dislike ");
  int num = keyboard.nextInt();

  int numA = num * 9;

  int numB = numA * 12345679;

  int numC = numB * 1000;






  System.out.println("                           ");
  System.out.println("                           " + num);
  System.out.println("                          X" + num);                       
  System.out.println("                ____________");
  System.out.println("                          " + numA);
  System.out.println("                   x" + 12345679);
  System.out.println("                ____________");
  System.out.println("Surprise           " + numB);       
  System.out.println("                       X" + 1000);
  System.out.println("                ____________");
  System.out.println("\"No Surprise\"?    " +  numC);

  }
  }

And this is what it is coming up with:

   Enter a number you dislike  9

                           9
                          X9
                ____________
                          81
                   x12345679
                ____________
Surprise           999999999
                       X1000
                ____________
"No Surprise"?    -727380968

I have absolutely no clue in this world how/why the final line came out to be "-727380968" Any help would be very appreciated.

Answer 1

This is probably overflowing int , which has a max value of around 2 billion. Try using long instead of int .

Here is the javadoc showing exactly the max value of an int : https://docs.oracle.com/javase/7/docs/api/java/lang/Integer.html#MAX_VALUE

Here is a quick link I found which shows why the underlying bit math turns a big number into something the computer reads as a negative number: https://www.cs.drexel.edu/~introcs/F2K/lectures/5_Scientific/overflow.html