Question

I’m supposed to write a program that asks for the number of rows the user wants. For example is the user entered 5 it will display all numbers from 25 to 1 arranged in 5 columns and 5 rows. Something like this should be the output if 5 is entered:

25  24  23  22  21
16  17  18  19  20  
15  14  13  12  11  
 6   7   8   9  10  
 5   4   3   2   1

As you can see there is a pattern. the first number to appear is the square of the number. then the next number is number squared minus 1. Until it reached 21, 5 will be subtracted bringing 16. Then it will add by 1 until it reach 20. As you can see it is like a snake.

The problem is it works for any number EXCEPT when 1 is entered. 0 is the current result when 1 is entered.

Here’s my current codes: please help me thanks

import java.util.*;
public class ArrayOutput2 
{
    public static void main(String[] args)
    {
        Scanner input = new Scanner(System.in);
        int number = 0;

        System.out.print("Enter number of rows: ");
        number = input.nextInt();

        int[][] num = new int[number][number];
        int k=1, i, j;

            while(k< (number*number))
            {
                for(i=number; i>=1; i--)
                {
                   if (i%2==1)
                   {
                     for(j=number-1; j>=0; j--)
                         {
                             num[i-1][j]=k;
                             k++;
                         }
                   }

                   else
                         for(j=0; j<=number-1; j++)
                         {
                             num[i-1][j]=k;
                             k++;
                         }
                 }
           }

        for(i=0;i<number;i++)
        {
             for(j=0;j<number;j++)

             System.out.print(num[i][j]+"\t");
             System.out.println();   
        }

    }
}

Answer 1

Suppose that the user inputs 1 as a value, therefore number == 1.
You allocate an array num[1][1], that is an array with only one possible cell, number[0][0]

Then the loop is initiated

k=1;
while (k<(number*number)); // which is like while(1<1*1)==FALSE

therefore the loop is never used. You can use:

1) Either a do-while loop to run the loop at least once
2) or add an if statement just after while() loop ends:

// Using an IF statement immediately after the unmodified while()
if (number==1)
{
   num[0][0]=1;
}


// or with a loop DO-WHILE
    do
    {
        for(i=number; i>=1; i--)
        {
           if (i%2==1)
           {
             for(j=number-1; j>=0; j--)
              {
                num[i-1][j]=k;
                k++;
              }
           }
           else
              for(j=0; j<=number-1; j++)
              {
                num[i-1][j]=k;
                k++;
              }
         }
   }while(k<(number*number));