# Nature of Code book (random walker)
**URL:** https://discourse.processing.org/t/nature-of-code-book-random-walker/28637
**Category:** Beginners
**Created:** [March 18, 2021, 12:38pm UTC](https://discourse.processing.org/t/nature-of-code-book-random-walker/28637 "2021-03-18T12:38:05Z")
**Posts on this page:** 8
**Page:** 1
### Author:  [@Ariadne](https://discourse.processing.org/u/Ariadne)
#### Post date: [March 18, 2021, 12:38pm UTC](https://discourse.processing.org/t/nature-of-code-book-random-walker/28637/1 "2021-03-18T12:38:05Z")
I have been trying to follow with the Nature Of Code processing book **in p5js**.
The following code does not work:
```auto
class Walker {
contructor() {
this.x = 250;
this.y = 250;
}
display() {
stroke(255);
point(this.x, this.y);
}
step() {
const random_choice = random(4);
switch (random_choice) {
case 0: {
this.x += 1;
break;
}
case 1: {
this.x -= 1;
break;
}
case 2: {
this.y += 1;
break;
}
case 3: {
this.y -= 1;
break;
}
}
}
}
let w;
function setup() {
createCanvas(500, 500);
w = new Walker(width, height);
}
function draw() {
//background(0);
w.display();
w.step();
}
```
> Sorry for the small description! I am currently in ahurry.
---
### Author:  [@Chrisir](https://discourse.processing.org/u/Chrisir)
#### Post date: [March 18, 2021, 1:30pm UTC](https://discourse.processing.org/t/nature-of-code-book-random-walker/28637/2 "2021-03-18T13:30:34Z")
this works, but is not good code
```auto
let x = 250;
let y = 250;
class Walker {
contructor() {
// x = 250;
/// y = 250;
}
display() {
stroke(0);
fill(0);
circle(x, y, 2);
}
step() {
let random_choice = int(random(4));
switch (random_choice) {
case 0: {
x += 1;
break;
}
case 1: {
x -= 1;
break;
}
case 2: {
y += 1;
break;
}
case 3: {
y -= 1;
break;
}
}
}
}
let w;
function setup() {
createCanvas(500, 500);
w = new Walker(width, height);
}
function draw() {
//background(0);
w.display();
w.step();
}
//
```
---
### Author:  [@GoToLoop](https://discourse.processing.org/u/GoToLoop)
#### Post date: [March 18, 2021, 1:36pm UTC](https://discourse.processing.org/t/nature-of-code-book-random-walker/28637/3 "2021-03-18T13:36:47Z")
> [@Ariadne](#):
>
> ` contructor() {`
You’ve mispelled **constructor()**: 😉
` constructor() {`
> **[constructor - JavaScript | MDN](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Classes/constructor)**
>
> The constructor method is a special method of a class for creating and initializing an object instance of that class.
---
### Author:  [@Chrisir](https://discourse.processing.org/u/Chrisir)
#### Post date: [March 18, 2021, 1:52pm UTC](https://discourse.processing.org/t/nature-of-code-book-random-walker/28637/4 "2021-03-18T13:52:02Z")
Yes. I feel stupid now… 😉
I also changed this: ` let random_choice = int(random(4));`
```auto
class Walker {
constructor() {
this.x = 250;
this.y = 250;
}
display() {
stroke(0);
point(this.x, this.y);
// circle(this.x, this.y,4);
}
step() {
let random_choice = int(random(4));
switch (random_choice) {
case 0: {
this.x += 1;
break;
}
case 1: {
this.x -= 1;
break;
}
case 2: {
this.y += 1;
break;
}
case 3: {
this.y -= 1;
break;
}
}
}
}
let w;
function setup() {
createCanvas(500, 500);
w = new Walker(width, height);
}
function draw() {
//background(0);
w.display();
w.step();
}
//
```
---
### Author:  [@GoToLoop](https://discourse.processing.org/u/GoToLoop)
#### Post date: [March 18, 2021, 1:57pm UTC](https://discourse.processing.org/t/nature-of-code-book-random-walker/28637/5 "2021-03-18T13:57:18Z")
> [@Chrisir](#):
>
> I also changed this: ` let random_choice = int(random(4));`
- JS offers a variety of keywords to declare variables w/.
- My fav is [`const`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/const) b/c most of the time variables don’t need to be re-assigned.
- B/c the variable _random\_choice_ is only accessed within _switch_’s parens we can simply eliminate the variable to shorten the code further:
```auto
step() {
// let random_choice = int(random(4)); // no need
switch (~~random(4)) {
```
---
### Author:  [@Chrisir](https://discourse.processing.org/u/Chrisir)
#### Post date: [March 18, 2021, 1:58pm UTC](https://discourse.processing.org/t/nature-of-code-book-random-walker/28637/6 "2021-03-18T13:58:41Z")
and I added `int()`
Chrisir
---
### Author:  [@Ariadne](https://discourse.processing.org/u/Ariadne)
#### Post date: [March 18, 2021, 3:06pm UTC](https://discourse.processing.org/t/nature-of-code-book-random-walker/28637/7 "2021-03-18T15:06:49Z")
Thank you! By the way, in your reply to @Chrisir, you code thefollowing:
```auto
step() {
// let random_choice = int(random(4)); // no need
switch (~~random(4)) {
```
can you say what this does?
---
### Author:  [@GoToLoop](https://discourse.processing.org/u/GoToLoop)
#### Post date: [March 18, 2021, 3:13pm UTC](https://discourse.processing.org/t/nature-of-code-book-random-walker/28637/8 "2021-03-18T15:13:48Z")
Using the unary bitwise operator [`~`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Bitwise_NOT) twice truncates a value by removing its fractional part.
It’s a shorter & more performant replacement for **int()**: 😛
[https://p5js.org/reference/#/p5/int](https://p5js.org/reference/#/p5/int)