Solved

java pascal triangle array program wont compile

Posted on 2009-07-12
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Last Modified: 2013-11-23
hi everyone,

this program is supposed to take a number 'rowCount' as input from a user, then use that number to create an equal number of rows in a pascal triangle. the code initializes pascal0[] and pascal1[] in the PascalTri class to remember values in the current (1) and previous (0) rows.
it's also supposed to print these rows to the console, but i must be doing something wrong because it hasnt worked. can anyone point me in the right direction?

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public class PascalTri{
 
        public int rowCount;
        int[] pascal1 = new int[0];
        int[] pascal0 = {};
 
        public PascalTri(int row){
            row = rowCount;
            for(int i=0; i<row; i++){
                pascal1[0] = 1;
                pascal1[pascal0.length] = 1;
                pascal1 = new int[pascal0.length+1];
                for(int j=1; j<pascal0.length;j++){
                    pascal1[j] = pascal0[j] + pascal0[j-1];
                }
                pascal0 = pascal1;
                }
            }
       
        public void displayRows(){
            System.out.println(pascal1);
        }
    }
 
=============================================================================
 
import java.util.Scanner;
 
    public class PascalDriver{
      public static void main(String[] args){
        Scanner scan = new Scanner(System.in);
        System.out.println("Enter number of rows");
        int rowCount = scan.nextInt();
        PascalTri t = new PascalTri(rowCount);
        t.displayRows();
      }
    }

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Question by:bpiche
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6 Comments
 
LVL 92

Expert Comment

by:objects
ID: 24836631
you need to use a loop in displayRows to display the triangle
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Author Comment

by:bpiche
ID: 24836649
how could I do that short of embedding the displayRows function within the PascalTri function?

thanks again
0
 
LVL 92

Expert Comment

by:objects
ID: 24836703
you need to use a 2d array, following shows how to use it with your current code

import java.util.Scanner;

public class PascalTri {

      int[][] pascal1 = null;

      public PascalTri(int row) {
            
            // create empty triangle
            
            pascal1 = new int[row][];
            
            // initialise first row
            
            pascal1[0] = new int[1];
            pascal1[0][0] = 1;
            
            // calculate remaining rows
            
            for (int i = 1; i < row; i++) {
                  pascal1[i] = new int[i+1];
                  pascal1[i][0] = 1;
                  pascal1[i][i] = 1;
                  for (int j = 1; j < pascal1[i].length; j++) {
                        int[] pascal0 = pascal1[i-1];
                        //pascal1[j] = ...;
                  }
            }
      }

      public void displayRows() {
            for (int i=0; i
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Author Comment

by:bpiche
ID: 24836768
is there any way i can do this without 2d arrays? sorry i forgot to mention that >.<
0
 
LVL 92

Accepted Solution

by:
objects earned 125 total points
ID: 24836774
you'd need to print it out as you calculate instead of printing it out from a separate method
0
 
LVL 20

Assisted Solution

by:a_b
a_b earned 125 total points
ID: 24837116
What  I would suggest is that you move the logic from the constructor of the PascalTri class to the displayRows(). Within displayRows(), run loops as shown below -

for(i=0;i<rowCount;i++)
{
     for(j=0;j<i;j++)
         //Print the values 1 upto rowCount
     for(j=i;j>0;--+)
         //Print the values from  rowCount down to 1
}

This is in a nutshell, you might have to fine tune the indexes just a bit.
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