打印带有嵌套循环的棋盘。 【JAVA]

Question

I'm having issues with getting my code to print. I need to print a checker board with a grid the size of a user input.

Example of what it should output.

Input a size (must be larger than 1):
5

0 *   *   *
1   *   *  
2 *   *   *
3   *   *  
4 *   *   *

Here's my code:

import java.util.Scanner;
public class nestedpractice1 
{
    public static void main(String[] args)
    {
        Scanner kbinput = new Scanner(System.in); 
        //Create Size variable
        System.out.println("Input a size: ");
        int n = 0; n = kbinput.nextInt();

        for(int r = 0; r < n; r++)
        {
            for(int c = 0; c < r; c++)
                    {
                if((r%2) == 0)
                {
                    System.out.print("*");
                }
                else if((r%1) == 0)
                {
                    System.out.print(" *");
                }
            }
            System.out.println("");
            kbinput.close();
        }
    }
}

My code keeps printing

**

****

Answer 1

By looking at your code, I found these potential issues:

• kbinput.close(); should not be called inside the loop.
• else if((r%1) == 0) should be else if (r % 2 != 0) , although in this case simply else is enough.
• in the else , you might want to do System.out.print(" ");
  instead of System.out.print(" *");
• I believe for(int c = 0; c < r; c++) { should loop as long as c < n .

Answer 2

This loop yields precisely the output you specified:

    for (int r = 0; r < n; r++) {
        System.out.print(r);
        for (int c = 0; c < n; c++) {
            System.out.print(r % 2 == 1 ^ c % 2 == 0 ? " *" : "  ");
        }
        System.out.println();
    }

I condensed the body of the inner loop to a single print statement. This statement uses the ^ (xor) operator to test for a condition, and then the ?: (ternary) operator to print an asterisk if the condition is true or spaces if the condition is false .

We could break up that single statement, while retaining its meaning, like so:

            boolean isOddRow = r % 2 == 1;
            boolean isEvenCol = c % 2 == 0;
            System.out.print(isOddRow ^ isEvenCol ? " *" : "  ");

As explanation, we want to print a * only if the row and column are both even or both odd. So if the row is even but the column is odd, or if the row is odd but the column even, we print only spaces.

We could express the same logic using == instead of ^ by:

            boolean isEvenRow = r % 2 == 0;
            boolean isEvenCol = c % 2 == 0;
            System.out.print(isEvenRow == isEvenCol ? " *" : "  ");

Or if you prefer the longhand if..else over the shorthand ternary operator:

            if (isEvenRow == isEvenCol) {
                System.out.print(" *");
            } else {
                System.out.print("  ");
            }