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introduction to touchdevelop statements o command, simple statement o var, local variable declaration o if … then … else o for each [var] in … where … do … o for 0 ≤ [var] < … do … o while … do o comments o do nothing

introduction to touchdevelop adding o tap one of the + in the statement menu o tap intended statement button

introduction to touchdevelop editing o first, enter condition/bound/ collection o tap the hardware back button when done

introduction to touchdevelop editing o to modify condition/bound/collection, select entire expression o to modify body, select statement in body

introduction to touchdevelop command o any expression is a statement o unassigned expression results are simply forgotten o use the store in var button to assign the value into a fresh local variable ☀ use to be called expression or do stuff…

introduction to touchdevelop var o very similar to the command but with a placeholder to store the expression value ☀ while var is mostly a syntactic sugar which automatically gets added when assigning into a fresh local, this button was introduced to reduce the confusion of beginners looking for the var keyword.

introduction to touchdevelop if … then … else o empty else-branch is shown in compact form, but cannot be removed o to edit condition, select the entire if then else block.

introduction to touchdevelop for each [var] in … where … do … o iterates over a collection actually equivalent to a loop from i :=0 to (collection→count-1), assigning collection→at(i ) to loop variable [var] in each iteration o iteration variable is automatically synthesized to rename it, use it in the body, tap on it, and rename o use ‘where’ clause to filter, if desired equivalent to ‘if’, but more efficient o example: for each song in media→ songs where song→duration > 180 do song→post to wall

introduction to touchdevelop demo / exercise ► let’s write this script: for each song in media→ songs where song→duration > 180 do song→post to wall

introduction to touchdevelop for 0 ≤ [var] < … do … o iterates from 0 (includes) to an upper bound (exclusive) o iteration variable is automatically synthesized to rename it, use it in the body, tap on it, and rename o example: for 0 ≤ i < 4 do i→post to wall prints

introduction to touchdevelop for 0 ≤ [var] < … do … o surprised by the ordering on the wall? try this: for 0 ≤ i < 4 do i→post to wall time→sleep(1)

introduction to touchdevelop while … do … o executes loop body while condition is true o example: i := 0 while i < 4 do i →post to wall i := i + 1 prints

introduction to touchdevelop demo / exercise ► let’s write this script: i := 0 while i < 4 do i →post to wall i := i + 1

introduction to touchdevelop scope o in the app, scope is indicated by indentation (and gray lines) o to add a statement in a particular scope, select an existing statement in that scope, and tap +

introduction to touchdevelop comments o comments do nothing o (unlike many other language, comments are maintained in the “abstract syntax tree” to play nice with the editor)

introduction to touchdevelop do nothing o empty place holder statement

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