Using Nested For Loops To Make Triangle

[Collin Sampson]

I am trying to make a program that prints a triangle made of asterisks with maximum length of user input:
So if the user inputs 5, it should look like this:
*
**
***
****
*****
****
***
**
*
I got my program to do the first loop, up until the maximum. I would appreciate some help on how to make it flip.
Is it a separate for-loop? Is it another, nested, for-loop?
Here is my code:

import java.util.*;

class TriangleProgram
{

	public static void main (String[] args)
	{
		System.out.println("Enter the size of a triangle, an integer from");
		System.out.println("1 to 50 please.");
		
		Scanner keyboard = new Scanner(System.in);
		
		int size;
		int x, y;
		int a, b;
		size = keyboard.nextInt( );
		
		for (x = 1; x <= size; x++) //number of loops to print
            {
             	for (y = 1 ; y <= x ; y++) //number of aestriks to print on a line
             		System.out.print("*");
             	System.out.println();
             	
            }        
	
	}
}

[Jeff Verdegan]

                for (y = 1 ; y <= x ; y++) //number of aestriks to print on a line  

So you already know how to define the number of starts in a row in terms of x for the top half of the shape. Since you can do that, I'd think you should be able to define the number of stars in a row in terms of x for the bottom half also. Write it out on paper if it helps you to see the pattern:

 row | numStars
-----+---------
  1        1
  2        2

and so on. We can see from the above that numStars = rowNum for the top half.

[Seetharaman Venkatasamy]

As Jeff said reverse the first part, x = size - 1 and x--

[Jeff Verdegan]

Seetharaman Venkatasamy wrote:As Jeff said reverse the first part, x = size - 1 and x--

Funny, I don't recall saying that, or giving him the code.

[Sarah Mitchell]

1- For such a program there must be a condition for a minimum number since we won't be able to draw a triangle if the user's input was 1. And also you should enforce the range from 1(or 2) - 50 by code so the user cannot get out of it. ( Check point 5 bellow for more details ).

2- I suggest using a JOptionPane to ask for the user's input, it would look a lot more professional .

3- For the loops you don't need anymore variables than just x, y.

4- And here, I was able to modify your code to get you what you want :

import java.util.Scanner;

public class Triangle {
    public static void main (String[] args)
    {
        System.out.println("Enter the size of a triangle, an integer from");
        System.out.println("1 to 50 please.");

        Scanner keyboard = new Scanner(System.in);
        int x, y;
        int size = keyboard.nextInt();
        
        for(x = 0; x <= size; x++){
            for(y = 0; y < x; y++){
                System.out.print("*");
            }
            System.out.println();
        }
        for(x = size-1; x >= 0; x--){
            for(y = x-1; y >= 0; y--){
                System.out.print("*");
            }
            System.out.println();
        }

    }

}

My advice would be to look at the code only, then try to re-create it yourself to get the maximum benefit and learn, otherwise you won't learn so much.

5- I made another version of the code one with if statement to ensure that the users enters a number >= 2 && <= 50. Just in case you're interested .

import java.util.Scanner;

public class Triangle {
    public static void main (String[] args)
    {
        System.out.println("Enter the size of a triangle, an integer from");
        System.out.println("1 to 50 please.");
  
        Scanner keyboard = new Scanner(System.in);
        int x, y;
        int size = keyboard.nextInt();

        if(size >= 2 && size <= 50){
            for(x = 0; x <= size; x++){
                for(y = 0; y < x; y++){
                    System.out.print("*");
                }
                System.out.println();
            }
            for(x = size-1; x >= 0; x--){
                for(y = x-1; y >= 0; y--){
                    System.out.print("*");
                }
                System.out.println();
            }
        }else{
        System.out.println("Your input must be between 2 - 50");
        }

    }
}

I hope I helped. Good Luck =)

[Jeff Verdegan]

Sarah Mitchell wrote:
4- And here, I was able to modify your code to get you what you want :

Please don't do that. This site is NotACodeMill.(⇐click) Doing somebody's work for him does not help him to learn. As it says on the topics page: "We're all here to learn, so when responding to others, please focus on helping them discover their own solutions, instead of simply providing answers."

[Collin Sampson]

Thanks for the help. I both wrote it out and looked at the code provided. Makes sense now.

row                    numStars

 1                     size -1

 2                     size -2

So... numStars = size -rowNum

initialization = size -1
boolean expression = numStars >= 0
change = numStars-- (one less star on each line)

[Seetharaman Venkatasamy]

Jeff Verdegan wrote:

Seetharaman Venkatasamy wrote:As Jeff said reverse the first part, x = size - 1 and x--

Funny, I don't recall saying that, or giving him the code.

Ahh, my bad time

[Sarah Mitchell]

Jeff Verdegan wrote:

Sarah Mitchell wrote:
4- And here, I was able to modify your code to get you what you want :

Please don't do that. This site is NotACodeMill.(⇐click) Doing somebody's work for him does not help him to learn. As it says on the topics page: "We're all here to learn, so when responding to others, please focus on helping them discover their own solutions, instead of simply providing answers."

Oops. I'm sorry I thought I'm helping !
Won't happen in the future, promise >.<

Collin Sampson wrote:Thanks for the help. I both wrote it out and looked at the code provided. Makes sense now.

row                    numStars

 1                     size -1

 2                     size -2

So... numStars = size -rowNum

initialization = size -1
boolean expression = numStars >= 0
change = numStars-- (one less star on each line)

Yes, but this only goes for the second half of the triangle, because if we didn't add the -1 there will be a duplication for the row in the middle, and I guess we don't want this. Right ?

[Seetharaman Venkatasamy]

Sarah Mitchell wrote: I'm sorry I thought I'm helping !
Won't happen in the future, promise

Apologies accepted