1. Doing things more than once
Loops
Doing things more than once
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2. Repetition So far we have: What we have not done is keep things moving
Designed scenes
Put actors in motion
Moved the parts as they were moving
What we have not done is keep things moving
They move then stop
What we want next is to repeat actions
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3. Again and Again In Computer Science we frequently use repetition
We call it:
Repetition
Looping
Iteration
Recursion
Academics always like big words
Alice must support iteration in the same easy way it handles everything
Looping is covered in the second month in a normal class
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4. Loop Types Alice has two types of loops The Loop is based on a count
Do something N times
The While loop is based on a condition
Do something while a condition is true
Both are containers like the Do Together
Either of these can keep things moving forever
Recall the ice skater
The model continues to blink after the rest of the animation is over
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5. Loop Container Count based
It will execute the statements that are contained within it
These are executed in order
The count may be:
A constant
An expression, such as a parameter
A math expression
Infinity
The Java For
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6. How is this used? Drag it where it is wanted
Set the number of times to loop
Drag the body of the loop statements into it
Next we will see three screen shots that do this:
Initial drag
Choosing a count
When complete
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10. More on the Loop Did you notice the Show Complicated button?
The Loop can just count a fixed amount of times or it can count in other ways
These items may be changed:
Start count value
End count value
Increment
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12. Last thoughts Both repetition statements may be used anywhere
May be used in the First Method or in any you have defined
They are containers like any other
Any container may contain any other
We could have a While in a Loop which is itself contained in another While
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13. Finally Use the Loop statement to keep things moving
If your actors move in straight lines then they will need to occasionally turn towards the center
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