CSC 1701BComputing: Science and

Creativity

LECTURE #17SNAP! REVIEW

Outline Types Variables Operators Control: sequence, selection, repetition Functions (block headings will be given) Lists

Types Character

Single character like A 5 or $ Digit

0 through 9 only

Number 123 -99 0.05

Word 1 or more characters, no space A_word

Cat !@#$ Sentence

One or more words with spaces

Variables and Scripts Names that can store values that change

May be global (known everywhere) like this:

Or a script variable known only in that script

Operators Some operators only allow

digits or numbers + - x / mod round

Some operators allow many types < = > BTW, case does not matter

Others allow a mix of types

Control Sequential

one block call after another

Selection if if…else

Repetition repeat until for

Selection and repetition can be nested You won’t need to write

nested control on the Midterm

Functions Functions take in 0 or

more inputs and return exactly 1 output

The same inputs MUST yield same outputs Output function of

input only

Other rules of functions No state (prior history) No mutation (no

variables get modified) No side effects

(nothing else happens)

CS Illustrated function metaphor

Domain The type “class” of input a

function accepts

Examples Sqrt of

Positive numbers Length of

Sentence, word, number _ < _

Both: Sentence, word, number

_ and _ Booleans

Letter _ of _ Number from 1 to input

length Sentence, word, number

Range All the possible return

values of a function

Examples Sqrt of

Non-negative numbers or Nan

Length of Non-negative integer

_ < _ Boolean (true or false)

_ and _ Boolean (true or false)

Letter _ of _ Letter

More Terminology (from Math)

Why use functions? (1)

The power of generalization!

Why use functions? (2) Functions can be composed together to

make even more magnificent things

Functions are the building blocks of almost everything we create when programming

Functional decomposition: the process of breaking big problems down into smaller tasks

Command No outputs Meant for side-effects Not a function… Not on Midterm

Reporter (Function) Any type of output

Predicate (Function) Only Boolean output

(true or false)

You will not need to write any block headings on the MidTerm

Types of Blocks

You will be asked to complete blocks on the midterm, given the block heading

Example: Complete this custom block to return the smaller of two values: write the text, use ( and )

if (a < b)

set smaller to a

else

set smaller to b

report smaller

Writing Snap! On Paper

would be written as ((a > b) and (a < 999))

Practice test question shows how to write Snap!

Writing Snap! On Paper

• We often need to store a collection of items

• Snap! has the list block• Found under Variables

• The following list has 3 elements• It is considered an anonymous list as it has no name

Lists

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By default, a list has 1 item that is an empty word

To create an empty list, click the left arrow to remove it

New lists can have one nothing ITEM

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A named list with 3 elements

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Give a name to an “empty” list, add 3 names Show all, first, last, and any element in the list

known as names

names is a list with zero elements

Other blocks you may need

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These will be added to the question ifthey will be needed (no need to memorize Snap blocks) length is # items in the list add adds at the end insert places a new thing

at the given index 1..length

delete removes the thing at the given index

No need to memorize blocks You will see needed blocks in other

questions on the Midterm Or they will be given for that problem

Give a preview of the practice test

And finally