Pascal triangle in java using array

import java.util.Scanner;
public class PascalTriangleUsingArray
{
   public static void main(String[] args)
   {
      Scanner sc = new Scanner(System.in);
      int num, a, b, arr[][], p;
      System.out.println("Please enter number of rows: ");
      num = sc.nextInt();
      p = num - 1;
      arr = new int[num][num];
      for(a = 0; a < num; a++)
      {
         for(b = 0; b <= a; b++)
            if(b == 0 || b == a)
               arr[a][b] = 1;
            else
               arr[a][b] = arr[a - 1][b - 1] + arr[a - 1][b];
      }
      System.out.println("Pascal's triangle: \n");
      for(a = 0; a < num; a++)
      {
         for(b = 0; b <= p; b++)
            System.out.print(" ");
         p--;
         for(b = 0; b <= a; b++)
            System.out.print(arr[a][b] + " ");
         System.out.println();
      }
      sc.close();
   }
}