CPSC120B - Day 0 Notes

If you are using the lab machines, need to switch to the Linux operating system
The windows machines on campus do not have Python
The computers in our classroom and in the first floor lab can boot into Windows or Linux
Restart the computer and use the arrow keys to select Ubuntu

Open a web page and go to the daily schedule
Note, your reading for the next class is listed here
The top of the course web page has a link to the textbook
Select ‘How to Think Like a Computer Scientist’ from the ‘Useful Info’ menu
Can modify and run programs in the book
There are questions at the end of each section, answer them to test if you undertand it before coming to class
You can ask questions at the beginning of class, or email me questions if you are too shy to speak up during class
Or even better, schedule an apointment to see me
If you just want to write some code, use the book’s Scratch ActiveCode
Click on the magnifiing glass in the navigation bar at the top and select ‘Scratch ActiveCode’

Let’s write our first program
```
import turtle
turtle.forward(100)
```
Click run
It draws a line
This is similar to the Foos, you are giving commands to the computer
In this case, you are commanding a tutle (the arrow) to move around the screen
The turtle draws lines whenever it moves, so you can use it to draw pictures.
Change the number and you change the distance the turtle moves
Note, the turtle always starts in the center and moves to the right
You can change the direction the turtle moves with turtle.left and turtle.right.
```
import turtle
turtle.left(90)
turtle.forward(100)
```
This is similar to the Foos, the commands are a sequence, in this case from top to bottom
Note, the order matters

What happens when you switch the order?

import turtle
turtle.forward(100)
turtle.left(90)

Can also move the turtle without drawing a line with turtle.up and turtle.down
Also note, the import turtle at the top is necessisary
Try removing it, and you get an error
The error gives you some information about what went wrong
It tells you that it doesn’t know what turtle is and on what line
Some other common errors
- don’t forget turtle.
- don’t forget the parentheses
- don’t misspell the commands (or turtle)