# Trouble understanding for loops!

**URL:** <https://discourse.processing.org/t/trouble-understanding-for-loops/15211>\
**Category:** Beginners\
**Tags:** homework\
**Created:** [November 4, 2019, 12:37am UTC](https://discourse.processing.org/t/trouble-understanding-for-loops/15211 "2019-11-04T00:37:10Z")\
**Posts on this page:** 6\
**Page:** 1

<div class="post-metadata">

**Author:** ![IsaiahZ](https://avatars.discourse-cdn.com/v4/letter/i/8c91f0/32.png) [@IsaiahZ](https://discourse.processing.org/u/IsaiahZ)\
**Post date:** [November 4, 2019, 12:37am UTC](https://discourse.processing.org/t/trouble-understanding-for-loops/15211/1 "2019-11-04T00:37:10Z")

</div>

I am making this “illusion” and instead of coding it how I currently have it I need to use for loops and I’m not sure how to implement it for this code. I’m new so I would really appreciate the help. I would also like to add more rotating lines instead of the four spaced HALF\_PI in angle apart.  
This is what I have so far:

```auto
float angle1 = 0;
float angle2 = HALF_PI;
float angle3 = PI;
float angle4 = PI+HALF_PI;

final int BLACK = 0;
final int RED = #F70A0A;

final float SPEED = 0.02;
final float ORB_SMALL = 10;
final float ORBIT_RAD = 50;
final float ORB_LARGE = 100;
final float ORB_HUGE = 150;
final float ORB_MASS = 200;
final float ORB_FIN = 250;

void setup(){
  size(500, 500);
}

void draw(){
  background(127);
  //Draws inner rotating lines
  stroke(RED);
  line(width/2+ORB_SMALL*sin(angle1), height/2+ORB_SMALL*cos(angle1),
      width/2+ORBIT_RAD*sin(angle1), height/2+ORBIT_RAD*cos(angle1));
  stroke(BLACK);
  line(width/2+ORB_SMALL*sin(angle2), height/2+ORB_SMALL*cos(angle2),
      width/2+ORBIT_RAD*sin(angle2), height/2+ORBIT_RAD*cos(angle2));
  line(width/2+ORB_SMALL*sin(angle3), height/2+ORB_SMALL*cos(angle3),
      width/2+ORBIT_RAD*sin(angle3), height/2+ORBIT_RAD*cos(angle3));
  line(width/2+ORB_SMALL*sin(angle4), height/2+ORB_SMALL*cos(angle4),
      width/2+ORBIT_RAD*sin(angle4), height/2+ORBIT_RAD*cos(angle4));
      
  //Draws Innermost-middle rotating lines
  stroke(RED);
  line(width/2+ORBIT_RAD*sin(-angle1), height/2+ORBIT_RAD*cos(-angle1),
      width/2+ORB_LARGE*sin(-angle1), height/2+ORB_LARGE*cos(-angle1));
  stroke(BLACK);
  line(width/2+ORBIT_RAD*sin(-angle2), height/2+ORBIT_RAD*cos(-angle2),
      width/2+ORB_LARGE*sin(-angle2), height/2+ORB_LARGE*cos(-angle2));
  line(width/2+ORBIT_RAD*sin(-angle3), height/2+ORBIT_RAD*cos(-angle3),
      width/2+ORB_LARGE*sin(-angle3), height/2+ORB_LARGE*cos(-angle3));
  line(width/2+ORBIT_RAD*sin(-angle4), height/2+ORBIT_RAD*cos(-angle4),
      width/2+ORB_LARGE*sin(-angle4), height/2+ORB_LARGE*cos(-angle4));
  
  //Draws inner middle rotating lines
  stroke(RED);
  line(width/2+ORB_LARGE*sin(angle1), height/2+ORB_LARGE*cos(angle1),
      width/2+ORB_HUGE*sin(angle1), height/2+ORB_HUGE*cos(angle1));
  stroke(BLACK);
  line(width/2+ORB_LARGE*sin(angle2), height/2+ORB_LARGE*cos(angle2),
      width/2+ORB_HUGE*sin(angle2), height/2+ORB_HUGE*cos(angle2));
  line(width/2+ORB_LARGE*sin(angle3), height/2+ORB_LARGE*cos(angle3),
      width/2+ORB_HUGE*sin(angle3), height/2+ORB_HUGE*cos(angle3));
  line(width/2+ORB_LARGE*sin(angle4), height/2+ORB_LARGE*cos(angle4),
      width/2+ORB_HUGE*sin(angle4), height/2+ORB_HUGE*cos(angle4));
      
  //Draws outermost middle rotating lines
  stroke(RED);
  line(width/2+ORB_HUGE*sin(-angle1), height/2+ORB_HUGE*cos(-angle1),
      width/2+ORB_MASS*sin(-angle1), height/2+ORB_MASS*cos(-angle1));
  stroke(BLACK);
  line(width/2+ORB_HUGE*sin(-angle2), height/2+ORB_HUGE*cos(-angle2),
      width/2+ORB_MASS*sin(-angle2), height/2+ORB_MASS*cos(-angle2));
  line(width/2+ORB_HUGE*sin(-angle3), height/2+ORB_HUGE*cos(-angle3),
      width/2+ORB_MASS*sin(-angle3), height/2+ORB_MASS*cos(-angle3));
  line(width/2+ORB_HUGE*sin(-angle4), height/2+ORB_HUGE*cos(-angle4),
      width/2+ORB_MASS*sin(-angle4), height/2+ORB_MASS*cos(-angle4));
     
  
  //Draws outer rotating lines
  stroke(RED);
  line(width/2+ORB_MASS*sin(angle1), height/2+ORB_MASS*cos(angle1),
      width/2+ORB_FIN*sin(angle1), height/2+ORB_FIN*cos(angle1));
  stroke(BLACK);
  line(width/2+ORB_MASS*sin(angle2), height/2+ORB_MASS*cos(angle2),
      width/2+ORB_FIN*sin(angle2), height/2+ORB_FIN*cos(angle2));
  line(width/2+ORB_MASS*sin(angle3), height/2+ORB_MASS*cos(angle3),
      width/2+ORB_FIN*sin(angle3), height/2+ORB_FIN*cos(angle3));
  line(width/2+ORB_MASS*sin(angle4), height/2+ORB_MASS*cos(angle4),
      width/2+ORB_FIN*sin(angle4), height/2+ORB_FIN*cos(angle4));
  
  //Change the angle each time
  angle1+=SPEED;
  angle2+=SPEED;
  angle3+=SPEED;
  angle4+=SPEED;
  
  //Draw circles with no fill
  for(int circle = 0; circle <=500; circle += 100){
    noFill();
    ellipse(width/2, height/2, circle, circle);
  }
  ellipse(width/2, height/2, 20, 20);
}

```

---

<div class="post-metadata">

**Author:** ![glv](https://yyz2.discourse-cdn.com/flex036/user_avatar/discourse.processing.org/glv/32/18785_2.png) [@glv](https://discourse.processing.org/u/glv)\
**Post date:** [November 4, 2019, 1:34am UTC](https://discourse.processing.org/t/trouble-understanding-for-loops/15211/2 "2019-11-04T01:34:36Z")

</div>

Hello,

To get you started:

```auto
float angle = 0; 

void setup()
  {
  size(500, 500);
  }

void draw()
  {
  background(127);
  translate(width/2, height/2);
  
  //Draw circles with no fill
  for (int circle = 0; circle <=500; circle += 100)
    {
    noFill();
    ellipse(0, 0, circle, circle);
    }

  ellipse(width/2, height/2, 20, 20);   
   
// Added
  pushMatrix();
  rotate(angle);
  for (int i= 0; i<= 100; i+=25)
    {
    noFill();
   pushMatrix();    
    rotate(i*TAU/100);
    line(50, 0, 100, 0);
   popMatrix();  
  }  
  popMatrix();
  
  angle+= TAU/300; //Added
  }

```

[https://processing.org/tutorials/transform2d/](https://processing.org/tutorials/transform2d/)  
[https://processing.org/tutorials/trig/](https://processing.org/tutorials/trig/)  
[https://processing.org/reference/TAU.html](https://processing.org/reference/TAU.html)  
[https://processing.org/reference/rotate\_.html](https://processing.org/reference/rotate_.html)

🙂

---

<div class="post-metadata">

**Author:** ![glv](https://yyz2.discourse-cdn.com/flex036/user_avatar/discourse.processing.org/glv/32/18785_2.png) [@glv](https://discourse.processing.org/u/glv)\
**Post date:** [November 4, 2019, 1:43am UTC](https://discourse.processing.org/t/trouble-understanding-for-loops/15211/3 "2019-11-04T01:43:33Z")

</div>

Also check out examples that come with Processing:

 ![image](https://canada1.discourse-cdn.com/flex036/uploads/processingfoundation1/original/2X/8/8ee29cb2e752dabde065edebc3536f8a86fb980a.png)

🙂

---

<div class="post-metadata">

**Author:** ![IsaiahZ](https://avatars.discourse-cdn.com/v4/letter/i/8c91f0/32.png) [@IsaiahZ](https://discourse.processing.org/u/IsaiahZ)\
**Post date:** [November 4, 2019, 1:44am UTC](https://discourse.processing.org/t/trouble-understanding-for-loops/15211/4 "2019-11-04T01:44:26Z")

</div>

Thank you. I have not learnt anything about push matrices or what TAU is. Also, what does the translating the width/2 and height/2 mean? Does that mean it sets width/2 and height/2 as the new origin point of sorts? Thank you though, this is all very helpful!

---

<div class="post-metadata">

**Author:** ![glv](https://yyz2.discourse-cdn.com/flex036/user_avatar/discourse.processing.org/glv/32/18785_2.png) [@glv](https://discourse.processing.org/u/glv)\
**Post date:** [November 4, 2019, 12:06pm UTC](https://discourse.processing.org/t/trouble-understanding-for-loops/15211/5 "2019-11-04T12:06:42Z")

</div>

Hello,

You can replace the push\pop and rotate with what you have done in your code already! It will require some modification to work with the **for loop** and increment **angle2** with each loop

And then add **angle** (see my example) to **angle2** (your code) and rotate the whole thing!

> [@IsaiahZ](#):
>
> line(width/2+ORB\_SMALL_sin(angle2), height/2+ORB\_SMALL_cos(angle2), width/2+ORBIT\_RAD_sin(angle2), height/2+ORBIT\_RAD_cos(angle2));

```auto
float angle = 0; 

void setup()
  {
  size(500, 500);
  }

void draw()
  {
  background(127);
  translate(width/2, height/2);
   
  //pushMatrix();
  //rotate(angle);
  for (int i= 0; i<= 4; i++)
    {
    noFill();
   //pushMatrix();    
    //rotate(i*TAU/4);
    // Modify and add your code here!
   //popMatrix();  
  }  
  //popMatrix();
  
  angle+= TAU/300; //Added
  }

```

You can look up all the references; if you highlight a keyword like **TAU** and right click and select “find in references” references that works too!

I prefer to use **TAU** as it represents **2\*PI** a full rotation; use what you are comfortable with here.

I feel that I have assisted too much already!  
Please try to understand what this is doing and work through this.

🙂

---

<div class="post-metadata">

**Author:** ![IsaiahZ](https://avatars.discourse-cdn.com/v4/letter/i/8c91f0/32.png) [@IsaiahZ](https://discourse.processing.org/u/IsaiahZ)\
**Post date:** [November 4, 2019, 3:35pm UTC](https://discourse.processing.org/t/trouble-understanding-for-loops/15211/6 "2019-11-04T15:35:37Z")

</div>

Thank you so much. This was all very very helpful!