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introduction to touchdevelop basic value types o Boolean true, false o Number IEEE floating point numbers, double precision o String there is no separate character type, consider using strings of length 1 o DateTime date + time

introduction to touchdevelop other types o All other types have “reference semantics” Values of all other types are references to actual data Copying values only copies references, not actual data o Examples: Song, Picture, … all collection types

introduction to touchdevelop ‘invalid’ o All types have an ‘invalid’ value Including Boolean, Number, String, DateTime For numbers, ‘invalid’ is different from NaN o To check if a value is null, use value→is invalid o To get an invalid value of a type, use invalid→[type name]

introduction to touchdevelop ‘invalid’ example var x := senses→current location if x→is invalid then “GPS not working”→post to wall time→stop

introduction to touchdevelop ‘invalid’ example var last := invalid→sprite for each current in my sprite set do if not last→is invalid then last→hide last := current current→show board→update on wall

introduction to touchdevelop collection types o there are many useful collection types o to create a new instance, use collections→create [collection type] o example: var c = collections→create location collection

introduction to touchdevelop special collections o number map mapping of Numbers to Numbers keys can be numbers different from 0, 1, 2, … ‘post to wall’ prints a chart o sprite set think of a simple “sprite collection” however, it is created from and belongs to a particular ‘board’

introduction to touchdevelop initial values o local variables get initial value from assignment expression example: x := 1 o parameters get initial value from calling context o returns are initially ‘invalid’ o global variables ( data) most are initially ‘invalid’ (!) however: Number: 0, Boolean: false, String: “”, Date: 1/1/0001

introduction to touchdevelop title o item 1 o item 2 song→post to wall ☀ anecdote ☁ (link to sample) ► an exercise ✿ a reference