# Nested for loops---help please!
**URL:** https://discourse.processing.org/t/nested-for-loops-help-please/24129
**Category:** Coding Questions
**Tags:** homework
**Created:** [September 26, 2020, 12:34am UTC](https://discourse.processing.org/t/nested-for-loops-help-please/24129 "2020-09-26T00:34:50Z")
**Posts on this page:** 18
**Page:** 1
### Author:  [@thughes](https://discourse.processing.org/u/thughes)
#### Post date: [September 26, 2020, 12:34am UTC](https://discourse.processing.org/t/nested-for-loops-help-please/24129/1 "2020-09-26T00:34:50Z")
I have an assignment that states the following–Create a program using nested for statements that will produce 5 rows, 7 in each column of diagonals as shown. You will need to size the frame 450 x 450. Determine your coordinates using that scale. Use a spreadsheet program to help you decide the x and y locations to draw the diagonals. You will need to create global variables to use in the line function. The nested for statement will loop through rows and columns.
I came up with the code to use, but i need to know how i can write the following code with nested for loops?
Also, each row of lines needs to be a different color…
size(450, 450);
strokeWeight(8);
fill(random(0,255), random(0,255), random(0,255));
int i=20;
int y1=40;
int y2=90;
for(i=20; i\<400; i +=60)
{
line(i, y1, i+60, y2);
line(i, y1+60, i+60, y2+60);
line(i, y1+120, i+60, y2+120);
line(i, y1+180, i+60, y2+180);
line(i, y1+240, i+60, y2+240);
}
---
### Author:  [@glv](https://discourse.processing.org/u/glv)
#### Post date: [September 26, 2020, 1:00am UTC](https://discourse.processing.org/t/nested-for-loops-help-please/24129/2 "2020-09-26T01:00:49Z")
Hello,
I see a pattern here that could be in a loop:
0, 60, 120, 180, 240
`:)`
---
### Author:  [@Hyperion65](https://discourse.processing.org/u/Hyperion65)
#### Post date: [September 26, 2020, 1:20am UTC](https://discourse.processing.org/t/nested-for-loops-help-please/24129/3 "2020-09-26T01:20:42Z")
Since the universe frowns upon giving complete solutions…
you already have much of what you need. maybe it helps if you think about painting pixels in a digital image, one after another. lets say the image is 20 x 20 pixels in size.
lets say you start at the upper left pixel. you will paint one pixel after another until you reach the end.
you can think of it as a single loop, counting from point #0 to point #399.
your “loop” would be:
```auto
i = 0
paint the pixel black
add 1 to i
repeat (until i = 399)
```
but you can also say: I paint each row - **within** each row I paint each pixel
```auto
i = 0 <- thats the rows
j = 0 <- thats the pixels in a certain row
paint the pixel black
add 1 to j
repeat (until j = 19)
add 1 to i (until i = 19)
repeat
```
that is what is missing in you approach imho
it is a loop within a loop
that’s what “they” mean when they say: use a **nested** loop
if you manage the line, then you will probably use that global variable for the co… 🙂
---
### Author:  [@glv](https://discourse.processing.org/u/glv)
#### Post date: [September 26, 2020, 3:25pm UTC](https://discourse.processing.org/t/nested-for-loops-help-please/24129/4 "2020-09-26T15:25:28Z")
Hello,
More resources:
[6.3- For Loop - Processing Tutorial - YouTube](https://www.youtube.com/watch?v=h4ApLHe8tbk)
[6.6- Nested Loops - Processing Tutorial - YouTube](https://www.youtube.com/watch?v=H7frvcAHXps)
[https://processing.org/reference/for.html](https://processing.org/reference/for.html)
`:)`
---
### Author:  [@thughes](https://discourse.processing.org/u/thughes)
#### Post date: [September 26, 2020, 4:13pm UTC](https://discourse.processing.org/t/nested-for-loops-help-please/24129/5 "2020-09-26T16:13:35Z")
I’ve looked at all of those and still can’t figure out how to write the code correctly
---
### Author:  [@glv](https://discourse.processing.org/u/glv)
#### Post date: [September 26, 2020, 4:33pm UTC](https://discourse.processing.org/t/nested-for-loops-help-please/24129/6 "2020-09-26T16:33:25Z")
Keep working at it.
- There is a simple example in the reference I provided to plot points.
- Build on that example and draw lines (diagonals?).
- Then modify to meet the requirements of you homework assignment.
- And then try to do it from scratch without an example.
Rename variables in loops to x and y or row and col if that helps.
This is an achievable exercise.
`:)`
---
### Author:  [@thughes](https://discourse.processing.org/u/thughes)
#### Post date: [September 26, 2020, 8:58pm UTC](https://discourse.processing.org/t/nested-for-loops-help-please/24129/7 "2020-09-26T20:58:06Z")
i did that, but i am still only getting one row of diagonal lines
int y1=40;
int y2=90;
for(int i=20; i\<400; i = i+60)
{
for(int j=0; j\<400; j = j+60)
{
line(i, y1, i+60, y2);
}
}
---
### Author:  [@Chrisir](https://discourse.processing.org/u/Chrisir)
#### Post date: [September 26, 2020, 9:12pm UTC](https://discourse.processing.org/t/nested-for-loops-help-please/24129/8 "2020-09-26T21:12:49Z")
You have to use both i and j
Think of a chess board where you have rows and columns. That’s why you use a nested for loop.
---
### Author:  [@glv](https://discourse.processing.org/u/glv)
#### Post date: [September 26, 2020, 9:14pm UTC](https://discourse.processing.org/t/nested-for-loops-help-please/24129/9 "2020-09-26T21:14:51Z")
Please format your code:
[https://discourse.processing.org/faq#format-your-code](https://discourse.processing.org/faq#format-your-code)
y1 and y2 are not changing so will always be writing over the same row.
There is an example here for you to think about:
[https://processing.org/reference/for.html](https://processing.org/reference/for.html)
println() is useful to see the values of variables in your code:
[https://processing.org/reference/println\_.html](https://processing.org/reference/println_.html)
`:)`
---
### Author:  [@thughes](https://discourse.processing.org/u/thughes)
#### Post date: [September 27, 2020, 12:00am UTC](https://discourse.processing.org/t/nested-for-loops-help-please/24129/10 "2020-09-27T00:00:36Z")
where do i use j in my code?
---
### Author:  [@glv](https://discourse.processing.org/u/glv)
#### Post date: [September 27, 2020, 12:14am UTC](https://discourse.processing.org/t/nested-for-loops-help-please/24129/11 "2020-09-27T00:14:25Z")
There is an example here for you to think about and it uses i and j:
[https://processing.org/reference/for.html](https://processing.org/reference/for.html)
`:)`
---
### Author:  [@thughes](https://discourse.processing.org/u/thughes)
#### Post date: [September 27, 2020, 12:23am UTC](https://discourse.processing.org/t/nested-for-loops-help-please/24129/12 "2020-09-27T00:23:17Z")
yeah, i get that…but i’m doing lines and not points…that doesn’t work for me
---
### Author:  [@Chrisir](https://discourse.processing.org/u/Chrisir)
#### Post date: [September 27, 2020, 6:01am UTC](https://discourse.processing.org/t/nested-for-loops-help-please/24129/13 "2020-09-27T06:01:00Z")
Make some experiments with your code, play with it
Run it, change it, run it again
---
### Author:  [@thughes](https://discourse.processing.org/u/thughes)
#### Post date: [September 27, 2020, 5:12pm UTC](https://discourse.processing.org/t/nested-for-loops-help-please/24129/14 "2020-09-27T17:12:07Z")
please help me figure out what to do
i’m trying to make 5 rows of diagonal lines…
each row has to be a different color…
i know i need to increase y1 and y2 by 60…
i just can’t figure out how to write it…
i can get the first row
```auto
size(450, 450);
strokeWeight(8);
stroke(random(0,255), random(0,255), random(0,255));
int i=20;
int y1=40;
int y2=90;
for(i=20; i<400; i +=60)
{
for(i=20; i<400; i +=60)
{
line(i, y1, i+60, y2);
}
}
```
---
### Author:  [@glv](https://discourse.processing.org/u/glv)
#### Post date: [September 27, 2020, 5:21pm UTC](https://discourse.processing.org/t/nested-for-loops-help-please/24129/15 "2020-09-27T17:21:14Z")
> [@glv](#):
>
> There is an example here for you to think about and it uses i and j:
> [https://processing.org/reference/for.html](https://processing.org/reference/for.html)
> [@thughes](#):
>
> yeah, i get that…but i’m doing lines and not points…that doesn’t work for me
A point is one end of a line.
The reference page for line() can be found here along with tutorials and examples:
[https://processing.org/](https://processing.org/)
`:)`
---
### Author:  [@Chrisir](https://discourse.processing.org/u/Chrisir)
#### Post date: [September 27, 2020, 5:37pm UTC](https://discourse.processing.org/t/nested-for-loops-help-please/24129/16 "2020-09-27T17:37:44Z")
> [@thughes](#):
>
> `line(i, y1, i+60, y2);`
Here you calculate your line.
Here you have to use i AND j
Think of a chess board.
Play with this line, change it and run the code and see what happens
---
### Author:  [@thughes](https://discourse.processing.org/u/thughes)
#### Post date: [September 27, 2020, 5:42pm UTC](https://discourse.processing.org/t/nested-for-loops-help-please/24129/17 "2020-09-27T17:42:53Z")
a bunch of mess! still cant figure it out
---
### Author:  [@Chrisir](https://discourse.processing.org/u/Chrisir)
#### Post date: [September 27, 2020, 8:49pm UTC](https://discourse.processing.org/t/nested-for-loops-help-please/24129/18 "2020-09-27T20:49:01Z")
solved now
thanks to all
Chrisir