Branching and Looping Examples, cont

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Branching and Looping Examples, contd
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Remember the generic triple jump world
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Lets change this to be interactive.
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User input functions in Alice

• ask user for a number
• ask user for yes or no
• ask user for a string

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• Start Alice and open genericTripleJump
• Look at world. my first method
• Note that the statements there form a linear
  sequence.
• We want to modify this algorithm.

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• The first step is to add an If/Else instruction
  to the method.
• Drag a copy of the If/Else tile from the bottom
  of the editor area.
• Drop it into the method just below the three jump
  instructions.

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Adding If/Else instructions

• When adding an If/Else, you will be prompted to
  choose between true and false as an initial
  value for the condition.
• This value is merely a placeholder.
• We will always replace this value with a Boolean
  expression of a condition we want to test.

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• Replace the placeholder condition in the If/Else
  instruction with a function.
• We need the function that will allow us to ask
  the user a yes/no question.

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• We want Alice to jump only if the user answers
  yes to our query.
• Need to move the instruction that causes Alice to
  jump to the If clause of our If/Else instruction.

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• genericTripleJumpWhile.a2w
• genericTripleJumpLoop.a2w

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A Sentinel Sailing Loop

• Sailboat will turn to face the object
• Will sail one meter forward
• This process continues until the sailboat is
  within 5 meters of the object
• While (NOT (the sailboat is within 5
  meters of the object))
• turn to face object
• move forward 1 meter

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A Sentinel Sailing Loop

• Lets create a sail to method that will work with
  any object.
• It should accept the target object as an input
  parameter.
• This will be similar to the way the primitive
  move method accepts direction and amount

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A Sentinel Sailing Loop

• Sailboat will turn to face the object
• Will sail one meter forward
• This process continues until the sailboat is
  within 5 meters of the object
• While (NOT (the sailboat is within 5
  meters of the object))
• turn to face object
• move forward 1 meter

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A Sentinel Sailing Loop

• Sailboat will turn to face the object
• Will sail one meter forward
• This process continues until the sailboat is
  within 5 meters of the object
• While (NOT (the sailboat is within 5
  meters of the object))
• turn to face object
• move forward 1 meter

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A Sentinel Sailing Loop

• Sailboat will turn to face the object
• Will sail one meter forward
• This process continues until the sailboat is
  within 5 meters of the object
• While (NOT (the sailboat is within 5
  meters of the object))
• turn to face object
• move forward 1 meter

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Lets generalize sailTo so that we can sail to
any object.
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