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Logo Lesson 3. TBE 540 Fall 2004 Farah Fisher. Prerequisites for Lesson 3. Before beginning this lesson, the student must be able to… Use simple Logo commands to make a shape. Create and edit a procedure. Use the following commands appropriately POTS SAVE LOAD. Objectives for Lesson 3.

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Logo lesson 3

Logo Lesson 3

TBE 540

Fall 2004

Farah Fisher


Prerequisites for lesson 3
Prerequisites for Lesson 3

  • Before beginning this lesson, the student must be able to…

    • Use simple Logo commands to make a shape.

    • Create and edit a procedure.

    • Use the following commands appropriately

      • POTS

      • SAVE

      • LOAD


Objectives for lesson 3
Objectives for Lesson 3

  • After completing this lesson, the student will be able to…

    • Move the turtle to any screen position.

    • Determine the turtle’s screen position.

    • Explain the term variable.

    • Create procedures with variable input, using MAKE and RANDOM.


Logo screen positions
Logo Screen Positions

  • The position of the Logo turtle on the screen is described by two numbers - a horizontal and a vertical coordinate.

  • The center of the screen is the turtle’s home. Its designation is [0 0], and all other coordinates are measured from there.

  • It is very much like graphing in algebra.


Logo screen positions1
Logo Screen Positions

  • The first of the two numbers describes the horizontal distance in turtle steps right or left of the center.

  • For example, in the position [10 15], the 10 represents 10 turtle steps to the right of the center.

  • In the position [-25 10], the -25 represents 25 turtle steps to the left of the center.


Logo screen positions2
Logo Screen Positions

  • The second of the two numbers describes the vertical distance in turtle steps above or below the center.

  • For example, in the position [10 15], the 15 represents 15 turtle steps above the center.

  • In the position [25 -10], the -10 represents 10 turtle steps below the center.


Guess the positions
Guess the Positions

  • Make your best guess about the positions. Click to see the answers.

2

1

4

3


Guess the positions1
Guess the Positions

  • Possible screen positions (depending on Logo version)

[-100 50]

2

1

[ 150 75]

4

[ 25 -25]

3

[0 -50]


Position commands
Position Commands

  • PR POS is the command used to print (in the command window) the current position of the turtle.

  • SETPOS [numbernumber] or SETXY (numbernumber) sets the position of the turtle.

  • SETX number changes only the first number

  • SETY number changes only the second number

  • HOME returns the turtle to [ 0 0 ]


Challenge
Challenge

  • What shape do you think would result from these commands (assume turtle starts at [0 0])? Click to see the answer.

    • SETPOS [ 0 25 ]

    • SETPOS [ 25 25 ]

    • SETPOS [ 25 0 ]

    • SETPOS [ 0 0 ] or HOME


Challenge1
Challenge

  • The commands make a square!

[0 25]

[25 25]

[25 0]

[0 0]


Logo variables
Logo Variables

  • A variable is a letter or word that represents a number that can vary (thus the term variable).

  • In Logo, variables often have a colon in front of the letter or word.

  • Sample Logo variables -

    • :L2 :WIDTH :NAME :X


Logo variables1
Logo Variables

  • Variables must be assigned a value.

  • The Logo command MAKE is often used to “fill up” a variable.

  • For example, the command below puts the number 17 into the variable called :NUM (notice the quote and lack of colon)

    MAKE “NUM 17


Logo variables2
Logo Variables

  • See if you can determine the final value of :Z after the commands below. (NOTE: * means multiply, / means divide)

  • MAKE “Z 25

  • MAKE “Z :Z * 2

  • MAKE “Z :Z + 10

  • MAKE “Z :Z / 2


Logo variables3
Logo Variables

  • :Z becomes 30 after several calculations.

  • MAKE “Z 25 (:Z starts at 25)

  • MAKE “Z :Z * 2 (:Z is multiplied by 2, :Z = 50)

  • MAKE “Z :Z + 10 (10 is added to :Z, :Z = 60)

  • MAKE “Z :Z / 2 (:Z is divided by 2, :Z = 30)


Logo variables4
Logo Variables

  • After you define the value of a variable, you can use it in Logo commands in place of any number.

  • Examples:

    • FD :X

    • RT :D2

    • REPEAT 4 [ FD :SIZE RT 90 ]


Random
RANDOM

  • Logo variables can also be filled with random numbers.

  • The RANDOM command returns a number from 0 to a set limit.

  • Example: RANDOM 10 returns a number between 0 and 9.

  • Example: 1 + RANDOM 100 returns a number between 1 and 100.


Random1
RANDOM

  • Examples of MAKE with RANDOM

  • MAKE “Z RANDOM 15

    • :Z becomes a number between 0 and 14

  • MAKE “H23 1 + RANDOM 10

    • :H23 becomes a number between 1 and 10

  • MAKE “LENGTH 10 + RANDOM 50

    • :LENGTH becomes a number between 10 and 59 (10 + 0 to 10 + 49)


Samples of procedures with variables make random
Samples of Procedures with Variables (MAKE/RANDOM)

  • A variable size SQUARE

    • TO SQUARE

    • MAKE “SIZE 10 + RANDOM 100

    • REPEAT 4 [FD :SIZE RT 90]

    • END


Samples of procedures with variables make random1
Samples of Procedures with Variables (MAKE/RANDOM)

  • A variable size TRIANGLE

    • TO TRIANGLE

    • MAKE “SIZE 25 + RANDOM 50

    • REPEAT 3 [FD :SIZE RT 120]

    • END


Samples of procedures with variables make random2
Samples of Procedures with Variables (MAKE/RANDOM)

  • A variable size RECTANGLE

    • TO RECTANGLE

    • MAKE “S1 25 + RANDOM 50

    • MAKE “S2 25 + RANDOM 100

    • REPEAT 2 [FD :S1 RT 90 FD :S2 RT 90]

    • END


Another way to fill a variable
Another Way to Fill a Variable

  • You can also fill up a variable by defining it when you “run” a procedure.

  • Look at this procedure:

    • TO SQUARE :S

    • REPEAT 4 [FD :S RT 90]

    • END

  • Somehow, the :S needs a value.


Another way to fill a variable1
Another Way to Fill a Variable

  • To start this procedure…

    • TO SQUARE :S

    • REPEAT 4 [FD :S RT 90]

    • END

  • …you would type SQUARE 50 or SQUARE 100 or SQUARE 87

  • The number you type after the procedure name fills the variable.


Another way to fill a variable2
Another Way to Fill a Variable

  • Another example:

    • TO TRIANGLE :F

    • REPEAT 3 [FD :F RT 120]

    • END

  • To draw a triangle with sides of 50, type TRIANGLE 50 to start the procedure.


Another way to fill a variable3
Another Way to Fill a Variable

  • Consider this example:

    • TO RECTANGLE :L :W

    • REPEAT 2 [FD :L RT 90 FD :W RT 90]

    • END

  • You would need two numbers after the name of the procedure (the first becomes :L and the second becomes :W):

    • RECTANGLE 50 100

    • RECTANGLE 40 40


Self check lesson 3
Self Check Lesson 3

  • In the screen below, what is the best estimate of the turtle’s position?

    • [-50 50]

    • [50 -50]

    • [50 50]

    • [-50 -50]


Self check lesson 31
Self Check Lesson 3

  • In the screen below, what is the best estimate of the turtle’s position?

    • [-50 50]

    • [50 -50]

    • [50 50]

    • [-50 -50]

50

-50


Self check lesson 32
Self Check Lesson 3

  • Which of the following could not be the name of a Logo variable?

    • :Z

    • :The Size

    • :SIZE

    • :B123


Self check lesson 33
Self Check Lesson 3

  • Which of the following could not be the name of a Logo variable?

    • :Z

    • :The Size {no spaces allowed}

    • :SIZE

    • :B123


Self check lesson 34
Self Check Lesson 3

  • What will be the value of :BIG after the Logo commands below?

  • MAKE “BIG 5

  • MAKE “BIG :BIG + 25

  • MAKE “BIG :BIG - 7


Self check lesson 35
Self Check Lesson 3

  • What will be the value of :BIG after the Logo commands below?

  • MAKE “BIG 5 {:BIG=5}

  • MAKE “BIG :BIG + 25 {:BIG=30}

  • MAKE “BIG :BIG - 7 {:BIG=23}


Self check lesson 36
Self Check Lesson 3

  • Suppose you want a randomly chosen number between 1 and 10. Which of the following would generate that number?

    • RANDOM 10

    • RANDOM 1 + 10

    • RANDOM 10 + 1


Self check lesson 37
Self Check Lesson 3

  • Suppose you want a randomly chosen number between 1 and 10. Which of the following would generate that number?

    • RANDOM 10 {0 TO 9}

    • RANDOM 1 + 10 {10.0 TO 10.999}

    • RANDOM 10 + 1


Self check lesson 38
Self Check Lesson 3

  • Suppose you have entered the procedure below. What would you type to use it to draw a SQUARE with sides of 50?

    • TO SQUARE :X

    • REPEAT 4 [FD :X RT 90]

    • END

  • SQUARE

  • SQUARE 50

  • TO SQUARE 50


Self check lesson 39
Self Check Lesson 3

  • Suppose you have entered the procedure below. What would you type to use it to draw a SQUARE with sides of 50?

    • TO SQUARE :X

    • REPEAT 4 [FD :X RT 90]

    • END

  • SQUARE

  • SQUARE 50

  • TO SQUARE 50


Try some exercises
Try Some Exercises

  • Practice with procedures at http://www.csudh.edu/fisher/tbe540/LW3A.htm

  • Check out screen positions at http://www.csudh.edu/fisher/tbe540/LW3.htm

  • Try the hand-on exercise at http://www.csudh.edu/fisher/tbe540/LEX3.htm


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