1. Nate Brunelle Today: Pseudo-Code
CS1110
Nate Brunelle
Today: Pseudo-Code

2. Questions?

3. Ambiguity Put the pot in the dishwasher
When we talk to computer, we give it some instruction
How to wash your hair
Lather
Rinse
repeat

4. Hair washing ambiguity
Don’t know when to stop
What am I rinsing?
Where am I lather
What should I repeat?
What is lathering anyway?

5. Repeating
Repeat 3 times: lather rinse Lather Repeat: Rinse

6. Repeat 3 times: lather rinse How to lather: wet your hair put shampoo in your hand repeat until your hair is foamy: run your hand through your hair

7. How to wash you hair

8. Pseudo-Code Code: write things in a way a computer can understand
Pseudo- Not quite
Pseudo-Code:
Not quit write so that a computer can understand
Good for expressing things unambiguously
But still using English to gloss over the details

9. Conditionals What if I’m out of shampoo? How to wash your hair:
if you are out of shampoo:
get more shampoo
repeat:
lather
rinse

10. Rules of Pseudo-Code Sequence Repetition = repeat something
We start with the instruction written at the top
We go in order, one instruction at a time
Each line is “one” thing to do
Repetition = repeat something
Repeat a fixed number of times (repeat 3 times)
Repeat Until something happens (repeat until hair is foamy)
Conditions/Decisions = maybe do something
Check something first
If there is no shampoo, then get some more
Named actions
“how to lather”
Definition = describe how to perform that action
Use = no go do that thing

11. Do this
Repeat 2 times: stand clap sit

12. Brush your teeth
Write pseudo-code instructions for brushing your teeth
Share with your neighbor, who will try to find a problem with it
Remember:
Sequence
Repetition
Conditionals
Named Actions

13. 3x+1
Let x be your age in years Let “the count” be 0 Repeat as long as x is not 1: add 1 to “the count” if x is even: divide x by 2 otherwise: multiply x by 3 and add 1 Clap “the count” many times

14. X = 18
X = 9
X = 28
X=14
X = 7
X = 22
X = 11
X = 34
X = 17
X = 52
X = 26
X = 13
X = 40
X = 20
X = 10
X = 5
X = 16
X = 8
X = 4
x = 2
X = 1

15. Variables In Math: In Statistics: In Programming:
A name that refers to a particular value
In Statistics:
A name for a thing that has one value, but we don’t know what it is
In Programming:
A named value that can vary over the course of doing something
x is a variable in the previous slide

16. Problem Programs cannot “reflect” on what they did
Let x be your age in years
Let “count” = 0
Repeat as long as x is not 1:
add 1 to “count”
if x is even:
divide x by 2
otherwise:
multiply x by 3 and add 1
Clap “count” many times

17. Bugs
Syntax
Semantic
Logical
Understandability

18. “Homework”