AutoLISP Tutorial 11: Adjusting Text Height Using the IF Function

AutoCAD offers a vast range of possibilities when it comes to design and drafting. Text annotations are crucial components in drawings, aiding in communication and clarity. But what if you want to quickly adjust text height to match your design preferences? Using AutoLISP, AutoCAD’s scripting language, we can craft a solution. In this tutorial, we will delve into a program that harnesses the power of the IF function to easily and efficiently control text height.

AutoLISP Tutorial 11: Adjusting Text Height Using the IF Function


In this exercise, you’ll be crafting a program that allows the user to define the text height for their AutoCAD drawings. However, there’s a catch! The text height value must be between 0 and 1. If the user provides an appropriate value, the program should set the text height accordingly in AutoCAD. But if the entered value exceeds the limit, the program should display a warning to the user.


  1. Start by prompting the user to enter a desired text height value. Remember, the value should be a real number (which includes decimals).
  2. Check if the provided value lies within the permissible range (between 0 and 1).
  3. If the value is within the range, apply this as the new text height in AutoCAD.
  4. If the value is outside the permissible range, provide the user with a warning message indicating the restriction.
  5. Display a confirmation or error message at the end of the execution.


  • Use the getreal function to obtain a numerical input from the user.
  • The IF function will be your primary tool to check the provided condition and to determine which set of commands to execute based on the input.

Good luck, and remember: clarity and simplicity in your code will ensure that your program runs smoothly and is easy for others to understand!

AutoLISP Tutorial 11 Solution: Adjusting Text Height Using the IF Function

Adjusting text height in AutoCAD drawings can greatly impact readability and the overall aesthetic of a design. Our program aims to allow users to easily modify the text height while ensuring that it stays within a certain range. Let’s dive into the solution and see how we can achieve this using the IF function in AutoLISP.

Complete Program:

(defun C:TUTO11( / txh1)
(setq txh1 (getreal “\nEnter text height between 0 and 1: “))
(if (<= txh1 1.0)
(setvar “textsize” txh1)
(princ “\nThe text height must be 1.0 or less” )


Line-by-line Explanation:

  • (defun C:TUTO11 ( / txh1)
    • This line begins the definition of our function named C:TUTO11. The / in the list indicates that txh1 is a local variable, which means it won’t interfere with any other variables outside this function.
  • (setq txh1 (getreal “\nEnter text height between 0 and 1: “))
    • Here, we’re using the getreal function to prompt the user to input a real number. The input value will be stored in our local variable txh1.
  • (if (<= txh1 1.0)
    • We’re initiating an IF statement. The condition we’re checking is whether the value of txh1 is less than or equal to 1.0.
  • (setvar “textsize” txh1)
    • If the condition of our IF statement is true (i.e., txh1 is <= 1.0), we use the setvar function to adjust the text size in AutoCAD to the value of txh1.
  • (princ “\nThe text height must be 1.0 or less” )
    • If the condition of our IF statement is false (i.e., txh1 is > 1.0), we display a warning message to the user, indicating that the input was outside the permissible range.
  • (princ)
    • Finally, we use the princ function to display a blank line, ensuring that our program’s output is neatly formatted.


Mastering AutoLISP’s conditional operations, like the IF function, empowers you to create more responsive and user-friendly tools for AutoCAD. By ensuring text heights are set appropriately, you can achieve both visual balance and clarity in your drawings. Keep exploring AutoLISP, and watch as your AutoCAD projects reach new heights of professionalism and precision!