Tutorials

AutoLISP Tutorial 9 : Using the cond Function

2 years ago
by R. Khouri

In our journey through AutoLISP, we often encounter situations where our programs need to make decisions based on certain conditions. The cond function provides a flexible way to handle multiple conditions sequentially. This tutorial will guide you through the process of harnessing the capabilities of the cond function in a real-world scenario. By the end, you’ll be more confident in creating decision-making constructs within your AutoLISP programs.

Objective

Your task is to create a program that asks the user a simple question about their intent to quit and save the active drawing in AutoCAD. Depending on the user’s response, the program should execute the appropriate action or provide feedback.

Instructions:

  1. Start your program by displaying a message asking the user if they want to quit and save the active drawing.
  2. Take the user’s input. They can enter either “Yes” or “No”, and they can use uppercase or lowercase letters.
  3. Using the cond function, evaluate the user’s response:
    • If the user enters “Y” (uppercase) or “y” (lowercase), the program should execute the “QUIT” command and save the drawing.
    • If the user enters “N” (uppercase) or “n” (lowercase), the program should not take any action and just move forward.
    • For any other input, the program should do nothing.
  4. Conclude the program.

Remember, the objective is to make use of the cond function to handle the different scenarios based on the user’s response. Ensure your program is efficient and easy for the user to interact with.

AutoLISP Tutorial 8 Solution: Using the cond Function

In this solution, we will walk through a simple AutoLISP program that harnesses the power of the cond function to evaluate user input. The program is designed to ask the user whether they would like to quit and save the active drawing in AutoCAD. Depending on the user’s response, it will perform a specific action or give a particular feedback.

Complete Program:

(defun C:Tuto9 ( / ans1)
(princ “\n”)(princ “Do you what to quit and save the active drawing”)
(setq ans1 (getstring “\nEnter Yes[Y] or No[N]: “))
(cond
((= ans1 “Y”)(command “QUIT” “y”))
((= ans1 “y”)(command “QUIT” “y”))
((= ans1 “N”))
((= ans1 “n”))
(t nil)
)
(princ)
)

Line-by-Line Explanation:

(defun C:Tuto9 ( / ans1)
Here, we are defining a new function named Tuto9. The / ans1 indicates that ans1 is a local variable within this function.

(princ “\n”)(princ “Do you what to quit and save the active drawing”)
These lines print a message to the user asking them if they wish to quit and save the active drawing.

(setq ans1 (getstring “\nEnter Yes[Y] or No[N]: “))
This line gets the user’s input in response to the question and stores it in the ans1 variable.

(cond
The cond function begins here. It is used to evaluate conditions in a particular sequence.

((= ans1 “Y”)(command “QUIT” “y”))
If the user’s input (ans1) is “Y”, this line executes the “QUIT” command with the argument “y”, effectively quitting and saving the drawing.

((= ans1 “y”)(command “QUIT” “y”))
Similarly, if the user’s input is “y”, the “QUIT” command with the “y” argument is executed.

((= ans1 “N”)) and ((= ans1 “n”))
These lines check if the user input is “N” or “n”, respectively. If either condition is true, the program simply continues without executing any command.

(t nil)
This is the default condition. If none of the above conditions are met, the program does nothing.

(princ)
This line concludes the function, signaling its end.

The cond function is a powerful tool in AutoLISP for evaluating multiple conditions sequentially. This tutorial provided a hands-on example of how it can be used in practical scenarios, such as user interaction. Mastering conditional constructs like cond can greatly enhance the flexibility and efficiency of your AutoLISP programs.

Conclusion of the Tutorial

Congratulations on completing this tutorial on the cond function in AutoLISP! With this knowledge, you can now write programs that effectively respond to varying conditions. Remember, the true power of a programming language is not just in its individual functions, but in how you combine them to solve real-world challenges. Continue practicing, and soon, you’ll find yourself mastering even more advanced topics in AutoLISP.