# P5: Iteration (for loops) Draw a vertical line. Now draw two parallel, now three…

Introducing for loops:

```for (var i=1; i<=10; i++)
{
println(i);
}
```

This draws 10 horizontal lines:

```for (var i=1; i<=10; i++)
{
line (10, i*10, width, i*10);
}
```

Change the color gradually using the counter i!
Generalize the formula using variables for the distance and the number of lines!There can be multiple instructions in the same loop:

```for (var i=0; i<50; i++)
{
line (0, i*10, width, i*10);
ellipse(10*i, i*10, 10, 10);
}
```

Make a more complex pattern using at least 3 for loops or multiple instructions in the same loop!You can add randomness to the order:

```for (var i=0;  i<50; i++)
{
line (0, i*10, width, i*10);
var posX = random(0, width);
ellipse(posX, i*10, 10, 10);
}
```

Create a composition with 12 randomly generated shapes, using iteration!

Create a gradient (drawing line by line)

# EMBEDDED ITERATION

What if you have to iterate on two dimensions?
This is an example using indexes as number of rows and columns.

In this way you have better control over the number of shapes that are being drawn.

```var rows = 8;
var cols = 12;
var circleDiameter = 40;
var distanceX = 30;
var distanceY = 30;

function setup()
{
createCanvas(400,300);
background(0);
stroke(18, 255, 233);

for (var r = 1; r<= rows; r++) {
for (var c = 1; c <= cols; c++) {
ellipse(c*distanceX, r*distanceY, circleDiameter, circleDiameter);
}
}
}
```

You can control other parameters too:

```var box_size = 11;
var box_space = 12;
var margin = 7;

function setup()
{
createCanvas(200, 200);
background(0);
noStroke();

// Draw gray boxes

for (var i = margin; i<height-margin; i += box_space){
if(box_size &gt; 0){
for(var j = margin; j<width-margin; j+= box_space){
fill(255-box_size*10);
rect(j, i, box_size, box_size);
}
box_size = box_size - 0.6;
}
}
```

## While loop

Sometimes you don’t know in advance how many times you want to iterate and/or you don’t need an loop counter (variable i). In these cases while loops can be handy. Make sure you exit condition is met at some point:

```function setup()
{
createCanvas(200,200);
background(255);
noStroke();

var w = width;

while (w > 0) {
fill(w);
ellipse(width/2,height/2,w,w);
w = w - 20;
}```