LISP for making a square
....
(setq d (getreal "\nInput size of square: "))
(setq p1 (getpoint "\nSelect center of Square: "))
(setq d1 (/ d 2))
(setq a1 (- (car p1) d1))
(setq a2 (- (cadr p1) d1))
(setq b1 (+ (car p1) d1))
(setq b2 (+ (cadr p1) d1))
(setq p2 (list a1 a2))
(setq p3 (list b1 b2))
(command "rectangle" p2 p3)....
I would also suggest using (getdist) instead of (getreal) for the size of the square. You can then, if you like, set the distance by picking two points on-screen, and if you use Imperial Architectural units or Fractional units, you can enter it in feet-inches-fractions or just fractions format.
Kent Cooper, AIA 
Accepted solution
I had just suggested corrections of things I noticed, but now I also see that you are missing the space after the slash in the localized variables list:
(defun c:SQ (/{space here}d d1 a1 a2 b1 b2 pl p2 p3)
And I would also suggest that you prevent unexpected results if you have running Osnap modes in effect and there are any other things in the vicinity that it might snap to:
(command "rectangle" "_non" p2 "_non" p3)
[which is easier in a simple routine like this than the other way, which would be to save the OSMODE System variable value, set it to 0, do the drawing part, then restore OSMODE to what it was before].
Kent Cooper, AIA
@CodeDing wrote:
....
And I can see that you put these in here for fun:
(type "Created by Aaron Cruz")
(type "1oz Gomme Syrup, 1/2oz Tequilla, 1/2oz White Rum, 1oz lemon juice, 1/2oz triple sec, 1oz gin, 1/2oz vodka, splash of Cola. Mix and call a day.")...so just to be clear (i don't know if you know or not already) but these strings you are passing to the (type ...) function, are returning the STR atom (for stings). Not sure if that part was intentional or not lol.
....
I had just ignored that, but if the idea is to have them shown at the Command line, the function needed would be (prompt) or one of those that start with (prin...).
Kent Cooper, AIA
I was also going to suggest the simplifications that:
1. You can set more than one variable within one (setq) function, and
2. A variable that is used only once may as well not be set as a variable, but its calculation just used directly where applicable, eliminating several variables.
But in the process of adjusting to demonstrate, it also occurred to me that you might like to see the square at its actual size as you go to specify its center, i.e. drag it into place. This does that by drawing it in the middle of the screen, then MOVEing it, leaving you in the Move command to place it.
(defun c:SQ (/ d d1 pl)
(setq
d (getdist "\nInput size of square: ")
p1 (getvar 'viewctr)
d1 (/ d 2)
); setq
(command
"_.rectang"
"_non" (list (- (car p1) d1) (- (cadr p1) d1))
"_non" (list (+ (car p1) d1) (+ (cadr p1) d1))
"_.move" "_last" "" "_non" p1
); command
); defun
Kent Cooper, AIA
