Welcome to this lesson on basic arithmetic operations in AutoLISP. Arithmetic operations are fundamental in any programming language, and AutoLISP is no exception. By the end of this lesson, you will have a solid understanding of how to perform basic arithmetic operations in AutoLISP.
Learning OutcomesUnderstanding basic arithmetic operations in AutoLISP is not just about performing simple calculations. These operations form the foundation of many complex algorithms and functions you’ll encounter as you delve deeper into programming with AutoLISP. Whether you’re designing a tool to calculate areas, estimating material costs, or simply adjusting object dimensions, arithmetic plays a crucial role. 
Learning these operations will:
 Enhance ProblemSolving Skills: Many CAD challenges can be broken down into a series of arithmetic steps. Mastering these will empower you to tackle more complex problems with ease.
 Facilitate Efficient Scripting: Being proficient in arithmetic operations ensures that you can write efficient and optimized LISP routines, reducing unnecessary computational overhead and speeding up your scripts.
 Broaden Application Horizons: With a solid understanding of arithmetic, you’ll be wellequipped to explore advanced topics like geometry, trigonometry, and algorithm optimization in AutoLISP.
 Improve Accuracy and Precision: In the world of CAD, accuracy is paramount. By mastering arithmetic operations, you can ensure that your scripts produce precise and reliable results, minimizing potential errors in design.
The basic Arithmetic Operations in AutoLISP
Addition in AutoLISP
To add two or more numbers in AutoLISP, you use the +
operator.
Syntax:
(+ number1 number2 … numberN) 
;
) is a comment.For testing the code in AutoCAD, there’s no need to include these comments.
(+ 3 4) ; This will return 7 
Points to remember:
 You can add as many numbers as you wish.
 Ensure that you place the
+
operator at the beginning, followed by the numbers you wish to add.
Subtraction in AutoLISP
To subtract numbers in AutoLISP, you use the 
operator.
Syntax:
( number1 number2 … numberN) 
Example:
( 8 3) ; This will return 5 
Points to remember:
 The first number is the minuend, from which other numbers (subtrahends) will be subtracted.
 Like addition, you can subtract multiple numbers by listing them after the

operator.
Multiplication in AutoLISP
To multiply numbers in AutoLISP, you use the *
operator.
Syntax:
(* number1 number2 … numberN) 
Example:
(* 6 4) ; This will return 24 
Points to remember:
 Multiplication works similarly to addition and subtraction. You can multiply as many numbers as you want.
 Ensure that the
*
operator is at the beginning, followed by the numbers you wish to multiply.
Division in AutoLISP
To divide numbers in AutoLISP, you use the /
operator.
Syntax:
(/ dividend divisor) 
Example:
(/ 12 4) ; This will return 3 
Points to remember:
 The first number is the dividend, and the second number is the divisor.
 Division in AutoLISP is between two numbers only.
 Always ensure the divisor is not zero to avoid errors.
Practical Examples
Now that we’ve covered the basic arithmetic operations, let’s see some practical examples:
Calculate the average of three numbers:
(defun average (a b c)(/ (+ a b c) 3) )(average 5 6 7) ; This will return 6 
Calculate the area of a rectangle:
(defun rectangleArea (length width) (* length width) )(rectangleArea 4 5) ; This will return 20 
Summary
In this lesson, we delved deep into basic arithmetic operations in AutoLISP:
 Addition using the
+
operator.  Subtraction using the

operator.  Multiplication using the
*
operator.  Division using the
/
operator.
Remember, these basic operations are the building blocks for more advanced mathematical and logical functions in AutoLISP. Mastering them will pave the way for you to create more sophisticated and powerful CAD tools and solutions.