CS 1110 Nate Brunelle Today PseudoCode Party Questions

CS 1110 Nate Brunelle Today: Pseudo-Code, Party

Questions?

Course structure • Concepts • “Turtle”

Ambiguity • “Put the pot in the dishwasher” • What we say to computers: Instructions • How to wash your hair? How to wash your hair: Lather rinse repeat

How to wash you hair: repeat: lather rinse Lather Repeat: rinse

How to wash you hair: repeat 3 times: lather rinse How to lather: wet your hair put shampoo in your hand repeat until hair is foamy: rub your hand through you hair

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

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

Rules of Pseudo-Code • Sequence = Do the highest line first, then perform them in order from top to bottom – Line = one “thing” to do • Repetition = repeat something – Fixed number of times : e. g. “repeat 3 times” – Until something happens: e. g. “until hair is foamy” • Conditions/Decisions = maybe do something – Check something first – If there is no more shampoo, then get more • Named actions = two parts: definition, use – Definition = how to do a thing – Use = when to do the thing defined

Party Repeat 2 times: Sing “Happy Birthday to you” Sing “Happy Birthday to Nathan” Sing “Happy Birthday to You” Clap

Do this Repeat 2 times: stand clap sit

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

3 x+1 Let x be your age in years let count start as 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 “the count” many times

Variables • In Math: – 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

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

Bugs • Syntax – Statement does not “parse” • Semantic – Grammatically correct, but nonsense • Logical – Means something, but not what you meant • Understandability – I said it, it makes sense, and it means what I meant, but no one else can understand it

• Syntax – Statement does not “parse” – Dog of by chicken for running video the – W 202 dkdljdkla 9**ls • Semantic – Grammatically correct, but nonsense – Colorless green ideas sleep furiously – Park your car upon the cloud. – 3 0

• Logical – Means something, but not what you meant – “double 5” vs “ 5+2” • Understandability – I said it, it makes sense, and it means what I meant, but no one else can understand it – The sign should have dashes between fish and and and chips. – Prandial soleation is gauche.

“Homework”