Array for going through checkboxes (Newby question)

Hi all,

I am trying to get a simple piece of code to work but it gives me an error

--Unknown property: "Checked" in "chk0"

I want the script to add the number of each checked checkbox to an empty array (see line 28)

I think my issue is that chk0 is a string in my script and thus I get the error.
This should be a simple error on my side but I am not sure how to fix it.

rollout Test "Test" width:300 height:803  ( --start of Rollout Exporter

	--INCLUDE USER INTERFACE HERE	
	button btn_test "Test" pos:[18,14] width:116 height:60 toolTip:"If 'overwrite name' option is not used; obj name of currently selected obj will be used"
	groupBox grp1 "Export Options" pos:[150,7] width:151 height:439
	checkbox chk0 ".max                         0" pos:[160,25]
	checkbox chk1 ".3DS                         1" pos:[160,50] width:137 height:23         
checked:true
	checkbox chk2 ".AI                            2" pos:[160,70] width:137 height:23
	checkbox chk3 ".DWG                        3" pos:[160,90] width:137 height:23 
	checkbox chk4 ".DXF                         4" pos:[160,110] width:137 height:23 checked:true
	checkbox chk5 ".STL                          5" pos:[160,130] width:137 height:23
	checkbox chk6 ".SAT                         6" pos:[160,150] width:137 height:23
	checkbox chk7 ".PxProj / .NXB          7" pos:[160,170] width:137 height:23
	checkbox chk8 ".FBX                         8" pos:[160,190] width:137 height:23 checked:true
	checkbox chk9 ".DAE                         9" pos:[160,210] width:137 height:23
	checkbox chk10 ".IGS                         10" pos:[160,230] width:137 height:23
	checkbox chk11 ".WIRE                     11" pos:[160,250] width:137 height:23
	checkbox chk12 ".W3D                      12" pos:[160,270] width:137 height:23
	checkbox chk13 ".FLT                        13" pos:[160,290] width:137 height:23
	checkbox chk14 ".OBJ                       14" pos:[160,310] width:137 height:23 checked:true
	checkbox chk15 ".HTR                       15" pos:[160,330] width:137 height:23
	checkbox chk16 ".ASE                       16" pos:[160,350] width:137 height:23
	checkbox chk17 ".WRL                      17" pos:[160,370] width:137 height:23
	checkbox chk18 ".DWF                   18" pos:[160,390] width:137 height:23

--BUTTON
on btn_Test pressed do(
Array_chkboxes=#() --Empty array

for i in 0 to 18 do(
	
	x = "chk" + i as string
	print x
	
	if x.checked == true then(
	append x array_chkboxes
	)

)
print array_chkboxes
)
)

createdialog Test

Thank you :)

-Maarten