TASM: error when trying to modify a constant with an instruction

I get "argument needs type override" error in TASM due to trying to increase a constant value. I also can't use variables, because then I can't simply add them to each other and get the "operand types do not much" error. Is there any way to increase a constant or add two variables? I've tried to use registers - I mean copying the constant to a register and then increase the register and it works, but this does not solve my problem. Thanks for any suggestions.

model tiny
.486
.stack 200h

.data
h = 50
w = 100
x = 10
y = 10
k1 = 15
k2 = 0

.code
start:
mov ah, 0      ; graphics mode
mov al, 13h 
int 10h

; main loop
mov cx, 50
pg:
push cx

; top line
mov cx, x+w    ; column
mov dx, y      ; row
mov al, k1     ; white
p1:
mov ah, 0ch    ; put pixel
int 10h
dec cx
cmp cx, x
jae p1

; bottom line
mov cx, x+w
mov dx, y+h 
mov al, k1    
p2: 
mov ah, 0ch 
int 10h
dec cx
cmp cx, x
ja p2

; left line
mov cx, x   
mov dx, y+h
mov al, k1     
p3: 
mov ah, 0ch    
int 10h
dec dx
cmp dx, y
ja p3 

; right line
mov cx, x+w
mov dx, y+h
mov al, k1     
p4:
mov ah, 0ch   
int 10h
dec dx
cmp dx, y
ja p4

; delay
mov cx, 01h
mov dx, 4240h
mov ah, 86h
int 15h

; top line
mov cx, x+w 
mov dx, y    
mov al, k2      
p5:
mov ah, 0ch   
int 10h
dec cx
cmp cx, x
jae p5

; bottom line
mov cx, x+w 
mov dx, y+h
mov al, k2      
p6: 
mov ah, 0ch    
int 10h
dec cx
cmp cx, x
ja p6

; left line
mov cx, x   
mov dx, y+h 
mov al, k2      
p7: 
mov ah, 0ch    
int 10h
dec dx
cmp dx, y
ja p7 

; right line
mov cx, x+w 
mov dx, y+h  
mov al, k2      
p8:
mov ah, 0ch    
int 10h
dec dx
cmp dx, y
ja p8     

pop cx
dec cx
cmp cx, 50
;inc x
;inc y
jna pg

mov ah,00      ; read keyboard
int 16h         

mov ah,00      ; text mode
mov al,03
int 10h

mov ah,4ch     ; exit
int 21h

end start

Solution

Your code needs these changes :

Convert your constants into variables
Because of the variables, you will need to split the additions.
Also, because of the variables, it's necessary to initialize the data segment.

Here is your code with the 3 changes (pointed by "arrows") :

.model small
.stack 200h

.data
h dw 50                   ;<=========================
w dw 100                  ;<=========================
x dw 10                   ;<=========================
y dw 10                   ;<=========================
k1 db 15                  ;<=========================
k2 db 0                   ;<=========================

.code
start:
mov ax, @data             ;<=========================
mov ds, ax                ;<=========================

mov ah, 0      ; graphics mode
mov al, 13h 
int 10h

; main loop
mov cx, 50
pg:
push cx

; top line
mov cx, x;+w    ; column  ;<=========================
add cx, w                 ;<=========================
mov dx, y      ; row
mov al, k1     ; white
p1:
mov ah, 0ch    ; put pixel
int 10h
dec cx
cmp cx, x
jae p1

; bottom line
mov cx, x;+w              ;<=========================
add cx, w                 ;<=========================
mov dx, y;+h              ;<=========================
add dx, h                 ;<=========================
mov al, k1    
p2: 
mov ah, 0ch 
int 10h
dec cx
cmp cx, x
ja p2

; left line
mov cx, x   
mov dx, y;+h              ;<=========================
add dx, h                 ;<=========================
mov al, k1     
p3: 
mov ah, 0ch    
int 10h
dec dx
cmp dx, y
ja p3 

; right line
mov cx, x;+w              ;<=========================
add cx, w                 ;<=========================
mov dx, y;+h              ;<=========================
add dx, h                 ;<=========================
mov al, k1     
p4:
mov ah, 0ch   
int 10h
dec dx
cmp dx, y
ja p4

; delay
mov cx, 01h
mov dx, 4240h
mov ah, 86h
int 15h

; top line
mov cx, x;+w              ;<=========================
add cx, w                 ;<=========================
mov dx, y    
mov al, k2      
p5:
mov ah, 0ch   
int 10h
dec cx
cmp cx, x
jae p5

; bottom line
mov cx, x;+w              ;<========================= 
add cx, w                 ;<=========================
mov dx, y;+h              ;<=========================
add dx, h                 ;<=========================
mov al, k2      
p6: 
mov ah, 0ch    
int 10h
dec cx
cmp cx, x
ja p6

; left line
mov cx, x   
mov dx, y;+h              ;<=========================
add dx, h                 ;<=========================
mov al, k2      
p7: 
mov ah, 0ch    
int 10h
dec dx
cmp dx, y
ja p7 

; right line
mov cx, x;+w              ;<=========================
add cx, w                 ;<=========================
mov dx, y;+h              ;<=========================
add dx, h                 ;<=========================
mov al, k2      
p8:
mov ah, 0ch    
int 10h
dec dx
cmp dx, y
ja p8     

pop cx
dec cx
cmp cx, 50
;inc x
;inc y
jna pg

mov ah,00      ; read keyboard
int 16h         

mov ah,00      ; text mode
mov al,03
int 10h

mov ah,4ch     ; exit
int 21h

end start

Now the filled rectangle The idea is to draw the horizontal line many times increasing y :

.model small
.stack 200h

.data
h dw 50
w dw 100
x dw 10
y dw 10
k1 db 15
k2 db 0

.code
start:
mov ax, @data
mov ds, ax

mov ah, 0      ; graphics mode
mov al, 13h 
int 10h

; main loop
mov cx, 50
pg:
push cx

; top line
mov cx, x;+w    ; column
add cx, w
mov dx, y      ; row
mov al, k1     ; white
p1:
mov ah, 0ch    ; put pixel
int 10h
dec cx
cmp cx, x
jae p1

pop cx
inc y         ;<============= NEXT HORIZONTAL LINE WILL BE DRAWN IN THE NEXT LINE.
dec cx
cmp cx, 50
;inc x
;inc y
jna pg

mov ah,00      ; read keyboard
int 16h         

mov ah,00      ; text mode
mov al,03
int 10h

mov ah,4ch     ; exit
int 21h

end start