AutoLISP basics for automation in AutoCAD - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Understanding AutoLISP Function Definitions

Which of the following AutoLISP function definitions correctly defines a function named square that returns the square of a number x?

A (defun square x (* x x))

B (defun square (x) (* x x))

C (defun square (x) (* x))

D (defun square (x) (x * x))

💡 Hint

Remember that defun requires parentheses around parameters and the function body must be a valid expression.

Option B correctly defines a function named square with one parameter x and returns x multiplied by itself.

Option B misses parentheses around parameters.

Option B has an incomplete multiplication expression.

Option B uses invalid syntax for multiplication.

❓ dax_lod_result

intermediate

AutoLISP List Processing Output

What is the output of the following AutoLISP code snippet?

(setq mylist '(1 2 3 4))
(car (cdr mylist))

AutoCAD

(setq mylist '(1 2 3 4))
(car (cdr mylist))

A 2

B 1

C 3

D 4

💡 Hint

Recall that car returns the first element of a list and cdr returns the rest of the list after the first element.

cdr of mylist returns (2 3 4). Then car of that is 2.

🔧 Formula Fix

advanced

Identify the Error in AutoLISP Code

What error will occur when running this AutoLISP code?

(defun add-two (a b)
  (+ a b c))

AutoCAD

(defun add-two (a b)
  (+ a b c))

A No error, returns sum of a and b

B Error: Missing closing parenthesis

C Error: Variable c is unbound

D Error: Function add-two not defined

💡 Hint

Check if all variables used in the function are defined or passed as parameters.

The variable c is used but not defined or passed, causing an unbound variable error.

❓ visualization

advanced

Best Visualization for AutoLISP Automation Results

You have a list of AutoLISP script execution times for different automation tasks. Which visualization best helps compare the performance of these tasks?

A Pie chart showing percentage of total time per task

B Scatter plot of execution time vs. task complexity

C Line chart showing execution time over multiple runs

D Bar chart showing execution time per task

💡 Hint

Think about which chart type clearly compares values across categories.

A bar chart clearly compares execution times across different tasks.

Pie charts show parts of a whole but are less precise for exact comparisons.

Scatter plots and line charts are better for relationships or trends over time.

❓ data_modeling

expert

Designing Data Structure for AutoLISP Automation Logs

You want to store AutoLISP automation logs with task name, start time, end time, and status. Which data structure best supports efficient querying by task and calculating duration?

A Hash table with task names as keys and log records as values

B Association list with task as key and list of logs as value

C Flat list of logs with each log as a property list containing keys and values

D List of lists: ((task1 start end status) (task2 start end status))

💡 Hint

Consider fast lookup by task name and easy access to log details.

A hash table allows fast lookup by task name and stores detailed log records, making querying and duration calculation efficient.

Lists and association lists are slower for lookups.

Practice

1. What is the main purpose of using AutoLISP in AutoCAD?
(defun) is often used to define what?

easy

A. To export drawings to other formats

B. To manually draw shapes faster

C. To automate repetitive tasks by defining functions

D. To change the color of objects automatically

Solution

1. Step 1: Understand AutoLISP purpose

   AutoLISP is designed to automate tasks in AutoCAD to save time and reduce errors.

2. Step 2: Recognize (defun) usage

   (defun) defines a function that can be run as a command to automate tasks.

3. Final Answer:

   To automate repetitive tasks by defining functions -> Option C

4. Quick Check:

   Automation = Functions with (defun) [OK]

Hint: AutoLISP automates tasks using functions with defun [OK]

Common Mistakes:

• Thinking AutoLISP changes colors automatically
• Confusing manual drawing speed with automation
• Assuming AutoLISP exports files

2. Which of the following is the correct syntax to define a function named drawSquare in AutoLISP?

easy

A. defun drawSquare () (command "RECTANGLE")

B. (defun drawSquare [] (command "RECTANGLE"))

C. (defun drawSquare () command "RECTANGLE")

D. (defun drawSquare () (command "RECTANGLE"))

Solution

1. Step 1: Recall correct function syntax

   AutoLISP functions start with (defun functionName () ...) using parentheses for parameters.

2. Step 2: Check command usage inside function

   The (command "RECTANGLE") is correctly inside the function body.

3. Final Answer:

   (defun drawSquare () (command "RECTANGLE")) -> Option D

4. Quick Check:

   Correct parentheses and command call = (defun drawSquare () (command "RECTANGLE")) [OK]

Hint: Use parentheses () for parameters in defun [OK]

Common Mistakes:

• Using square brackets [] instead of parentheses
• Missing parentheses around defun
• Omitting parentheses around command

3. What will be the output when running this AutoLISP code?

(defun c:test ()
  (command "LINE" '(0 0) '(10 0) "")
  (princ "Line drawn")
)

medium

A. Draws a line from (0,0) to (10,0) and prints 'Line drawn'

B. Nothing happens because function is not called

C. Draws a circle instead of a line

D. Syntax error due to incorrect quotes

Solution

1. Step 1: Analyze the function definition

   The code uses (defun c:test () ...) to define a command named TEST, but does not call or execute it.

2. Step 2: Understand command and output

   Running this code only defines the function. No line is drawn, and no message is printed because the body is not executed. To run it, type TEST or (c:test).

3. Final Answer:

   Nothing happens because function is not called -> Option B

4. Quick Check:

   defun defines, does not run [OK]

Hint: defun defines functions/commands; they must be called to execute [OK]

Common Mistakes:

• Thinking function runs automatically without calling
• Confusing quotes causing syntax errors
• Assuming wrong command draws circle

4. Identify the error in this AutoLISP function:

(defun c:drawLine ()
  (command "LINE" (0 0) (10 10) "")
  (princ "Done")
)

medium

A. Points should be quoted lists, not bare numbers

B. Missing closing parenthesis for defun

C. Command name should be lowercase

D. princ cannot print strings

Solution

1. Step 1: Check point format in command

   AutoLISP requires points as quoted lists like '(0 0), not bare numbers (0 0).

2. Step 2: Verify parentheses and commands

   Parentheses are balanced, command name case is not an error, and princ prints strings correctly.

3. Final Answer:

   Points should be quoted lists, not bare numbers -> Option A

4. Quick Check:

   Points need quotes for lists [OK]

Hint: Use single quotes for coordinate lists '(x y) [OK]

Common Mistakes:

• Using unquoted coordinates causing errors
• Assuming case sensitivity for commands
• Thinking princ can't print strings

5. You want to create an AutoLISP function that draws a rectangle with width 20 and height 10 starting at point (5,5). Which code correctly automates this task?

hard

A. (defun c:drawRect ()
(command "RECTANGLE" '(5 5) '(25 15))
(princ "Rectangle drawn")
)

B. (defun c:drawRect ()
(command "RECTANGLE" (5 5) (20 10))
(princ "Rectangle drawn")
)

C. (defun c:drawRect ()
(command "RECTANGLE" '(5 5) '(20 10))
(princ "Rectangle drawn")
)

D. (defun c:drawRect ()
(command "RECTANGLE" '(0 0) '(20 10))
(princ "Rectangle drawn")
)

Solution

1. Step 1: Calculate rectangle corner points

   Starting at (5,5), width 20 means x=25, height 10 means y=15, so opposite corner is (25 15).

2. Step 2: Check correct point format and command

   Points must be quoted lists '(x y). (defun c:drawRect () (command "RECTANGLE" '(5 5) '(25 15)) (princ "Rectangle drawn") ) uses correct points and syntax.

3. Final Answer:

   (defun c:drawRect () (command "RECTANGLE" '(5 5) '(25 15)) (princ "Rectangle drawn") ) -> Option A

4. Quick Check:

   Correct points and quotes = (defun c:drawRect () (command "RECTANGLE" '(5 5) '(25 15)) (princ "Rectangle drawn") ) [OK]

Hint: Calculate corner points, use quoted lists '(x y) [OK]

Common Mistakes:

• Using unquoted points causing errors
• Using width/height as points instead of coordinates
• Starting rectangle at wrong point