Computer Science and Software Engineering© 2014 Project Lead The Way, Inc. Algorithms: Branching...
-
Upload
augustus-harvey -
Category
Documents
-
view
215 -
download
0
Transcript of Computer Science and Software Engineering© 2014 Project Lead The Way, Inc. Algorithms: Branching...
Computer Science and Software Engineering © 2014 Project Lead The Way, Inc.
Algorithms:Branching and Iteration
(in Scratch)
http://scratch.mit.edu/projects/11516969/
Learn from Scratch!
Edit your picture in paint editor
Algorithms are step-by-step procedures
If-else structure: conditional
• Always evaluates condition at top of the if-else structure
• Boolean expression: true or false
If-else structure• Executes one
chunk or the other
• If-else always executes one chunk: not zero, not two
• If (no else) might execute one or zero chunks
If-else structure
• Continues with next block
Stacked if-else-structures• These are separate structures,
one after another
-240
240
-240
2400 x
y
snapsing
snapsqueak
clapsqueak
clapsing
Nested if-else-structures• One inside the
other
-240
240
-240
2400 x
y
snapHello
clapHello
squeakFella
singFella
Iteration• Iteration: an algorithm that repeats,
one cycle after another
Your turn!
Don’t miss the “else” opportunity• These stacks run slightly differently.
Why?Usually wasteful, risky
Better
Pair of opposite conditions
How to get exactly-one-of-several• If-else selects 1-of-2• If-elseif-else selects 1-of-3
10 20 30
How to get exactly-one-of-several• How about 1-of-4?
1-of-3
10 20 30
1-of-4 ?if
else-if
else-if
else
if
else-if
else
How to get exactly-one-of-several1-of-5
10 20 30
if
else-if
else-if
else
40
else-if