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Note	The first character of the string for SUBSTR is number 1. However, other functions that process
	elements of a list (such as NTH) count the first element as 0.

Table 34-3 offers you a few more functions that work with numbers and strings.

	Table 34-3: AutoLISP Functions for Numbers and Strings
Function	Description
ABS	Returns the absolute value of the argument. (ABS -76) returns 76.
ASCII	Returns the ASCII code of a character. (ASCII “B”) returns 66.
CHR	Returns the text string for an ASCII code. (CHR 66) returns “B”. (Stands for
	character.)
ATOI	Converts a string to an integer. (ATOI “2.7”) returns 2. (Stands for ASCII to integer.)
ATOF	Converts a string to a real number. (ATOF “7.6”) returns 7.6. (Stands for ASCII to
	float, as in floating point — that is, a real number.)
ITOA	Converts an integer to a text string. (ITOA 76) returns “76”. (Stands for integer
	to ASCII.)
RTOS	Converts a real number to a text string, enclosed in quotes. You can add a mode
	(1=scientific, 2=decimal, 3=engineering, 4=architectural, 5=fractional) and a
	precision. Otherwise, RTOS uses the current settings. (RTOS 87.3 2 2) returns “87.30”.
	(RTOS stands for real to string.)
=	Equal to. Returns T for true if all arguments are numerically equal. (= 3 3.0)
	returns T. If the arguments are not equal, it returns nil.
/=	Not equal to. Returns T if all arguments are not numerically equal. (/= 5 6)
	returns T. If they are equal, it returns nil.
<	Less than. Returns T if each argument is numerically less than the next argument.
	Otherwise returns nil.
>	Greater than. Returns T if each argument is numerically greater than the next
	argument. Otherwise returns nil.
>=	Greater than or equal to. Returns T if each argument is numerically greater than
	or equal to the next argument. Otherwise returns nil.
<=	Less than or equal to. Returns T if each argument is numerically less than or
	equal to the next argument. Otherwise returns nil.

Using AutoLISP on the Command Line

You can use AutoLISP on the fly in AutoCAD because it is interpreted. By typing an expression on the command line, you get the result immediately. An interpreted language is one in which a single source statement is translated to machine language, executed, and then each subsequent source statement is operated on in the same way. This enables interactive entry of AutoLISP code into AutoCAD.

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The output of an AutoLISP expression can be used in response to AutoCAD prompts as well. For example, you can type (+ 1 7) at the Diameter/<Radius>: prompt of the CIRCLE command for a circle with a radius of 8 units. This capability to place AutoLISP expressions into AutoCAD commands is a very powerful tool.

If you leave out a closing parenthesis, AutoCAD returns (_> when you press Enter. This tells you that one open parenthesis has not been closed. If two open parentheses remain to be closed, AutoCAD responds with ((_>. Just type the correct number of closing parentheses at the command line and press Enter. AutoCAD accepts the expression.

STEP-BY-STEP: Working with Numbers and Text on the Command Line

1.Open a new drawing using any template.

2.Type circle . Follow the prompts:

Specify center point for circle or [3P/2P/Ttr (tan tan radius)]: Pick

any point.

Specify radius of circle or [Diameter]: (– 5 3)

AutoCAD draws a circle with a radius of 2.

3.Type (strcat “This is an example of “ “regular text.”) . Don’t forget the space between of and the quotation mark. When the two phrases are put together, this creates the space between of and regular. AutoCAD returns “This is an example of regular text.”

4.Press the up-arrow key. AutoCAD repeats the last line. Press the left-arrow key to move

to the right of the last r in regular and press Backspace to delete the word regular. Type italic . AutoCAD returns the new string concatenation.

5.Save the drawing in your AutoCAD Bible folder as ab34-02.dwg.

Note	When you create AutoLISP expressions on the command line or in the Console window, they
	aren’t saved with the drawing. They have the same status as any input you type at the com-
	mand line.

Creating AutoLISP Files

	If you want to use your AutoLISP expressions more than a couple of times, you should save
	them in a file. Create the routine in Visual LISP and choose Save File.
Tip	A common practice is to consolidate all AutoLISP routines in one folder for ease of use. To do
	this, you can create a folder called LISP in any drive or folder where you keep files that you
	create and then choose Tools Options. On the Files tab, expand the Support File Search
	Path and click Add. Add the path by typing it directly in the edit box or clicking Browse and
	navigating to it.

Because AutoCAD can open multiple drawings, you need to organize your AutoLISP routines based on whether you want them to apply to all drawings or just the first drawing you open.

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AutoCAD offers two LSP files that you can use for your AutoLISP routines:

acad.lsp: Use this file for routines that customize the initialization of AutoCAD. acad. lsp is not automatically loaded for every consecutive drawing. For example, if you want to load a special menu for only a specific drawing, you could put the routine in acad.lsp. (You can choose to load acad.lsp with every drawing. Choose Tools Options and click on the System tab. In the General Options section, check the Load acad.lsp with Every Drawing check box.)

acaddoc.lsp: Use this file for routines that customize the initialization of individual drawings. This file is loaded every time a drawing is opened. If you have a menu that contains AutoLISP macros that include variables you want available for all your drawings, put the AutoLISP routines used by the menu in acaddoc.lsp.

Each drawing contains its own AutoLISP environment. AutoLISP files you load in one drawing — and their variables — won’t be accessible to another drawing. To share functions, use (vl-load-all “filename”) instead of (load “filename”), where filename is the name of the AutoLISP file, to “populate” every current drawing, as well as any new drawing you may create. The VL-LOAD-ALL function is equivalent to placing an AutoLISP routine in acaddoc.lsp.

To create a new Visual LISP file, open the Visual LISP Editor (choose Tools AutoLISP Visual LISP Editor) and choose New File on the Standard toolbar. Visual LISP opens an

untitled document, as shown in Figure 34-8. You can now start typing code in the new document. When you start typing, you immediately notice that your code looks different than it would if you had typed it in a text editor — it’s in color! Visual LISP has the capability to distinguish certain features in your code and colors it accordingly. Table 34-4 lists the colors and their meanings.

Figure 34-8: A new AutoLISP document in the Visual LISP editor.

1000 Part VII Programming AutoCAD

Table 34-4: Visual LISP Editor Coloring System
Color	AutoLISP Syntax Element
Blue	Built-in functions and protected symbols
Magenta	Text strings
Green	Integers
Teal	Real numbers
Purple on gray background	Comments
Red	Parentheses
Black	Unrecognized items, such as variables you’ve created

If you want, you can customize these colors. From the Visual LISP menu, choose Tools Window Attributes Configure Current. In the Window Attributes dialog box, choose an element from the drop-down box and pick a color from the color swatches. You can also change the left margin and the tab width in this dialog box.

STEP-BY-STEP: Creating a New Visual LISP File

1.Start a new drawing using any template. You shouldn’t have any other drawings open.

2.Choose Tools AutoLISP Visual LISP Editor.

3. Choose New File from the Visual LISP Standard toolbar.

4.Type the following:

draws a horizontal line 3 units long (defun c:line3 (/ pt)

(princ "Please pick a point: ") (setq pt (getpoint))

(command "_line" pt "@3,0" "")

)

5.Select the first line of text and choose Comment Block from the Tools toolbar.

6.Choose Format Edit Window from the Tools toolbar to format the code.

7.Choose Check Edit Window and look at the result in the Build Output window.

8.Click the Visual LISP Editor to activate it again.

9.Choose Load Active Edit Window to load the routine.

10.Choose Activate AutoCAD from the View toolbar.

11.On the command line, type line3 .

12.At the Please pick a point: prompt, use any method to specify a point. AutoCAD draws a horizontal line 3 units long.