AutoCAD Tutorials

(April 1999)AutoLISP has many predefined functions to allow you to control your programs. Some of these functions are what are known as "relational" operators, and some are known as "conditional" operators.Relational operatorsNote: Arguments in brackets [] are optional.= (= atom atom ...)(= 3 2) ;Returns nil(= 3 3) ;Returns T(= 3 3 3) ;Returns TDetermines if a … [Read more...] about AutoLISP Lesson 7 – PROGRAM CONTROL

Mathematical expression formatAutoLISP uses a prefix notation for evaluating math expressions. The normal way you write equations is using an infix notation. If you wanted to add two numbers you would write it:1 + 2 = XIn AutoLISP it would be written as:(+ 1 2) ;Returns 3As you should know by now, all lists in AutoLISP start with a function and the remainder of the list is … [Read more...] about AutoLISP lesson 6 – NUMBERS

(April 1999)An AutoLISP program can be written many ways, but there are certain structural points that are common to all programs. Here you will learn how to put together a program, structured in the manner that best suits your current application.One of the main differences between programming in AutoLISP and programming in other languages, is AutoLISP is an interpreted … [Read more...] about AutoLISP Lesson 4 – PROGRAM FORMAT

(April 1999)Variables are used as the principle means to store values. Files may also be used to store values, but variables are what store values for short-term use.AutoLISP variables may be any of (4) four "types"; integers, reals, points, or strings. Variables in AutoLISP are automatically "typed" depending on the value they contain, so no "typing" of variables is … [Read more...] about AutoLISP Lesson 5 – VARIABLES

(April 1999)Why comment? In the lifecycle of a program there will be times when it is necessary to make changes, comments should be viewed as a revision and quality control function. Comments should only be written to aid in the later modification of the program or to find out what version of a particular program or function is currently being used. A good comment states … [Read more...] about AutoLISP Lesson 3 – COMMENTS

(April 1999)The AutoLISP environment is entered when AutoCAD receives a "(" symbol at the command line. When AutoCAD sees the opening parentheses, it runs the AutoLISP interpreter. The interpreter then evaluates, as a list, what is between the opening "(" symbol and the closing ")" symbol.Data typesThere are three basic data types in AutoLISP. They are functions, symbols, and … [Read more...] about AutoLISP Lesson 2 – THE AutoLISP ENVIRONMENT