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UCBLogo (University of California, Berkeley Logo) uses a simple, Lisp-like syntax with a focus on turtle graphics and recursion. Below is an overview of its syntax and key features.

Syntax

1. Basic Commands

FORWARD 100    ; Move forward by 100 units
BACK 50        ; Move backward by 50 units
RIGHT 90       ; Turn right by 90 degrees
LEFT 45        ; Turn left by 45 degrees

2. Drawing Shapes

Draw a Square

REPEAT 4 [ FORWARD 100 RIGHT 90 ]
  • REPEAT 4 [...] repeats the commands inside the brackets 4 times.

Draw a Triangle

REPEAT 3 [ FORWARD 100 RIGHT 120 ]

3. Variables & Math

Set a Variable

MAKE "x 50  ; Create variable x with value 50
PRINT :x    ; Print value of x

Basic Arithmetic

PRINT 2 + 3
PRINT 10 * 5
PRINT 100 / 4
PRINT 10 - 3

4. Procedures (Functions)

Defining and Using a Procedure

TO SQUARE :SIZE
    REPEAT 4 [ FORWARD :SIZE RIGHT 90 ]
END

SQUARE 50  ; Call the function with SIZE=50
SQUARE 100 ; Call the function with SIZE=100
  • TO starts a function definition.
  • :SIZE is a parameter.
  • END marks the function’s end.

5. Recursion (Fractals & Trees)

Recursive Tree

TO TREE :SIZE
    IF :SIZE < 5 [ STOP ]
    FORWARD :SIZE
    RIGHT 30
    TREE :SIZE * 0.7
    LEFT 60
    TREE :SIZE * 0.7
    RIGHT 30
    BACK :SIZE
END

TREE 100
  • Uses recursion to create a branching tree.

6. Looping (Alternative to REPEAT)

While Loop with Conditional

MAKE "count 0
WHILE :count < 5 [
    PRINT :count
    MAKE "count :count + 1
]

7. Conditional Statements

If-Else Condition

TO CHECK :NUM
    IF :NUM > 10 [ PRINT "Greater than 10" ]
    IF :NUM <= 10 [ PRINT "Less or equal to 10" ]
END

CHECK 15
CHECK 8

8. User Input

PRINT [Enter a number:]
MAKE "num READ
PRINT [You entered:] PRINT :num

9. Turtle Control

Pen Up / Down

PENUP    ; Stop drawing
FORWARD 50
PENDOWN  ; Resume drawing

Change Pen Color

SETPC [255 0 0]  ; Red color (RGB)

Change Background Color

SETBG 3  ; Set background color (number varies per system)

10. Clearing and Resetting

CLEARSCREEN   ; Clear the screen
HIDETURTLE    ; Hide the turtle
SHOWTURTLE    ; Show the turtle

Final Notes

  • UCBLogo is case-insensitive.
  • Commands can be shortened (FD for FORWARD, RT for RIGHT, LT for LEFT).
  • Comments are written with ;.

Would you like examples of something specific? 🚀

Circle

In UCBLogo, you can draw a circle using the REPEAT command with small movements and turns. Since Logo does not have a built-in CIRCLE command, you approximate a circle by making small steps in a loop.

Method 1: Using REPEAT

REPEAT 360 [ FORWARD 1 RIGHT 1 ]
  • This makes the turtle move forward 1 unit and turn 1 degree, completing a full 360-degree circle.

Method 2: Adjusting Size

To make a larger circle, increase the forward movement:

REPEAT 360 [ FORWARD 2 RIGHT 1 ]
  • This creates a larger circle by moving 2 units per step.

Method 3: Using a Procedure

You can create a function to draw circles of different sizes:

TO CIRCLE :RADIUS
    REPEAT 360 [ FORWARD :RADIUS * 0.017 RIGHT 1 ]
END

CIRCLE 10   ; Small circle
CIRCLE 50   ; Large circle
  • The :RADIUS * 0.017 scales the movement to maintain a circular shape.

Method 4: Using ARC (If Available)

Some Logo implementations support an ARC command:

ARC 360 50  ; 360-degree arc with radius 50
  • Not all UCBLogo versions have this feature.

Would you like a more complex shape, like a spiral or a flower pattern? 🚀

Pen

In UCBLogo, you can move the turtle without drawing by using PENUP (PU) before moving and PENDOWN (PD) to resume drawing.

Example: Move Without Drawing

PENUP    ; Lift the pen (no drawing)
FORWARD 100  ; Move forward without drawing
PENDOWN  ; Put the pen down (resume drawing)
FORWARD 50   ; This part will be drawn

Alternative Short Commands

  • PU = PENUP
  • PD = PENDOWN

Example: Move to a Specific Position

PENUP
BACK 50
RIGHT 90
FORWARD 50
LEFT 90
PENDOWN
  • Moves the turtle back and to the right without drawing.
  • Resumes drawing at the new position.

Would you like a way to teleport the turtle instantly to a position? 🚀

Clear

In UCBLogo, you can clear the page using the following commands:

1. CLEARSCREEN (CS)

CLEARSCREEN

or the shorthand:

CS
  • Clears the screen and moves the turtle back to the center (home position).

2. ERASING WITHOUT MOVING THE TURTLE

CLEAN
  • Erases all drawings but keeps the turtle in its current position.

3. RESET EVERYTHING

CLEARALL
  • Clears the screen, resets all variables, and completely restarts the environment.

Would you like to clear only specific parts of the screen instead? 🚀

TO CIRCLE :RADIUS
    REPEAT 360 [ FORWARD :RADIUS * 0.017 RIGHT 1 ]
    END