AutoLISP Tutorial 14: Drawing Lines with Conditional Loops

This program is used to demonstrate the if and the while functions. We’ll specifically focus on how to harness the power of conditional statements and loops to enhance user interaction. Even if you’re a beginner, by the end of this tutorial, you’ll be able to create an interactive program to draw lines in AutoCAD based on user input. Let’s dive in!

AutoLISP Tutorial 14: Drawing Lines with Conditional Loops

Hello students! For today’s exercise, we are going to embark on an interactive journey where you will be tasked with creating a program that enables users to draw lines within their drawing environment.

Objective

Your goal is to create a program where users can input multiple points to draw lines continuously. The drawing session should end when the user presses “Enter” without specifying a point.

Steps to consider:

Prompt the user to specify the first point.
Create a loop that allows users to continuously input the next point to extend the line.
Make sure the program recognizes when the user wants to stop drawing (i.e., by pressing “Enter” without specifying a point).
Once the drawing session is terminated, the program should gracefully exit without any errors.

Keep these steps in mind and utilize your knowledge of the if and while functions to achieve this functionality. Remember to focus on user interaction and think about the process flow of drawing multiple lines.

AutoLISP Tutorial 14 Solution: Drawing Lines with Conditional Loops

Hello learners! Let’s dive into the solution for the given task. In this exercise, we have to implement a program that allows a user to draw lines using the input points until the user decides to stop.

The Complete Program

(defun C:tuto14 ( / stp1 pnt1 pnt2)
(setq pnt1 (getpoint “\nEnter the first point: “))
(setq stp1 0)
(while (= stp1 0)
(setq pnt2 (getpoint pnt1 “\nEnter next point: “))
(if (= pnt2 nil)
(setq stp1 1)
(progn
(command “LINE” pnt1 pnt2 “”)
(setq pnt1 pnt2)
)
)
)
(princ)
)

Line-by-Line Explanation

(defun C:tuto14 ( / stp1 pnt1 pnt2)
This line starts the definition of our function named “tuto14”. We’re also declaring three local variables: stp1, pnt1, and pnt2.

(setq pnt1 (getpoint “\nEnter the first point: “))
Here, we are prompting the user to input the first point for drawing, and storing this point in the variable pnt1.

(setq stp1 0)
This sets the control variable stp1 to 0, which will be used in our loop to determine when the user wants to stop drawing.

(while (= stp1 0)
Initiates a while loop which continues running as long as stp1 is equal to 0.

(setq pnt2 (getpoint pnt1 “\nEnter next point: “))
Inside our loop, we prompt the user to specify the next point. This point is relative to the last point (pnt1) entered.

(if (= pnt2 nil)
Checks if the user pressed “Enter” without specifying a point. If so, the pnt2 will be nil.

(setq stp1 1)
If the user pressed “Enter”, we set stp1 to 1, indicating the loop should stop.

(progn
A progn function is used to group multiple expressions together. In this context, it allows us to execute multiple commands if pnt2 is not nil.

(command “LINE” pnt1 pnt2 “”)
This line commands AutoCAD to draw a line from the point pnt1 to the point pnt2.

(setq pnt1 pnt2)
After drawing the line, we update the pnt1 variable with the value of pnt2 for the next iteration of the loop.

(princ)
This line ends our function and returns a nil value, suppressing any unwanted output.

Conclusion

By the end of this tutorial, You’ve now learned how to integrate conditional statements and loops into your AutoLISP programs, allowing for more dynamic and interactive functionalities in AutoCAD, you should have gained a deeper understanding of how to use if and while loops within AutoLISP to interactively draw lines. This hands-on exercise is essential for understanding user input and iterative processes in AutoCAD automation. Keep practicing and always think about the user experience!