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Alice Workshop Functions, Loops, and Parameters

Alice Workshop Functions, Loops, and Parameters. Do in order dragon flies to princess princess climbs on dragon's back dragon and princess escape knight shakes his arm (and sword) in protest. dragon takes off. Where are we?.

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Alice Workshop Functions, Loops, and Parameters

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  1. Alice WorkshopFunctions, Loops, and Parameters

  2. Do in order dragon flies to princess princess climbs on dragon's back dragon and princess escape knight shakes his arm (and sword) in protest dragon takes off Where are we? • Thus far, we have written object-level methods for the dragon • flapWings • takeOff • fly

  3. Next • Now, the dragon must fly to the princess • Break it down into simple steps: Do in order fly to the princess dragon turn into a position that will allow princess to climb on board

  4. World-level method • This method clearly involves two different objects: • dragon • princess • We will write a world-level method rather than a object-level method. General rule of thumb: If more than one object is involved in a method, write the method as a world-level method.

  5. turn to face

  6. Loop • The fly method moves the dragon forward 1 meter. • We want to call the fly method repeatedly to move the dragon to the princess. • Alice has a Loop statement.

  7. Problem • The problem is: How many times should the fly method be called? ?

  8. Functions • Alice has several built-in distance functions, that can be used to determine the number of meters objects are from one another. • In this example, the Loop should execute once for each meter of this distance.

  9. Behind the scenes • To be truthful, • Loop needs a whole number (e.g., 4) • The distance in front of function returns a double number (e.g., 4.37 meters) • Behind the scenes, Alice truncates the distance to a whole number

  10. Complete Methods

  11. Animation:Smooth, Continuous Movement • For most purposes, execution of an instruction works best with a gentle slowdown in speed (toward the end of the duration) • Successive repetitions, however, may have a smoother continuous motion if made to end abruptly

  12. Animation:Smooth, Continuous Movement • For most purposes, execution of an instruction works best with a gentle slowdown in speed (toward the end of the duration) • Successive repetitions, however, may have a smoother continuous motion if made to end abruptly

  13. Object-level method with parameters • We could also write this method for the dragon object • But it still involves two objects in the world • dragon • princess • We must use a parameter in order to access the princess from the dragon method

  14. Create a object-level method Name it flyToPerson

  15. Parameters • A parameter is a shared element that conveys information between one method and another • A parameter, has a name, a value, and a type • Type describes the kind of information that is shared • Click on create new parameter button

  16. Parameters • Name the object "who” (or something else appropriate) • Select the Object type then click OK

  17. Use the parameter • Turn the dragon to face …

  18. What is a Variable? • A variable is an element in a program to store values that are likely to change as the program executes • Also useful for • Naming values that may be abstract • Allowing code to be more readable • Decomposing a complex process into a series of simpler processes

  19. Create a variable in a method

  20. Like Parameters • Variables have a name (distanceToWho) • Variables have a type (Number)

  21. Parameters vs. Variables • Both parameters and variables • Have a name • Have a type (which describes the kind of data being stored) • Store values that can change as the program runs • Parameters carry values from one method to another • Variables belong to one particular method only (local)

  22. Using a variable • Drag the variable tile into the code editor • Select a value for the variable

  23. Using the function with parameter • To set the value of the variable

  24. Using the variable in the loop

  25. Code

  26. Text • For more information • Functions and Expressions • Chapters 3 and 6 • Loop • Chapters 3 and 7 (Section 1) • Methods and Parameters • Chapter 4 • Variables • 10-1

  27. Do in order princess climbs on dragon's back dragon and princess escape knight shakes his arm (and shield) in protest dragon takes off dragon flies to princess Your turn… • Write code to have the • princess climb onto the dragon's back (not climb, actually – just move to the dragon) • dragon and princess escape from the castle (use vehicle) Experts

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