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The general shape of a Stack block.

A Stack block is a rectangular block that is shaped to fit above and below other blocks. Stack blocks make up the majority of the blocks available in Scratch, being available in every category except Operators and PicoBoard Blocks.

When 2 stack blocks are connected to form a script their commands will run from top to bottom, unless turbo mode has been activated in which case the script runs all blocks at the same time.

Blocks

There are 77 stack blocks in Scratch 2.0, including extensions, as follows:

Shape

Stack blocks are fitted with a puzzle-piece like shape; the top has a notch and the bottom has a bump. Because of this shape, scripts can stretch on and on — the block tessellates.

Their shape allows them to be placed in the following areas:

when gf clicked
say [Hi.] for (2) secs
  • Before/after other Stack blocks
go to [Sprite2 v]
play sound [meow v] until done
point towards [Sprite3 v]
say [Bye.] for (2) secs
stop [this script v]
forever 
if <(loudness) > (30)> then
say [No noises.] for (2) secs

Use

As Stack blocks are shaped to allow blocks above and below them, they are used almost everywhere in a script; scripts must always have a Stack block in them to be functional. An example script:

when flag clicked
repeat until <(do_Stop) = [1]>
move (10) steps
change [color v] effect by (25)
play sound [meow v] until done
if <touching [edge v]?> then
say [Done!] for (2) secs
stop [this script v]
end
end

Note how the Stack blocks are used in the script — they make up all the commands.