You would need to include irvine16.inc or add a stack directive. 

;;comments start with semi colons:
;;this longwinded program prints good morning or good afternoon

.code

Timepromt db ‘is it afternoon?(y/n)$’

GoodMorningMessage  LABEL  BYTE
   DB  13,10,'Good morning, world!',13,10,'$'
Go odAfternoonMessage  LABEL  BYTE
   DB  13,10,'Good afternoon, world!',13,10,'$'
   .CODE
   main proc near
mov ax,@data
mov ds,ax                                ;set DS to point to the data segment
mov dx,OFFSET TimePrompt                ;point to the time prompt
mov  ah,9                                 ;DOS print string function #
int  21h                 &n bsp;                ;display the time prompt
mov  ah,1                                 ;DOS get character function #
int  21h                 &n bsp;                ;get a single-character response
cmp al,'y'                               ;typed lowercase y for after noon?
jz IsAfternoon              &nbs p;           ;yes, it's after noon
cmp al,'Y'                               ;typed uppercase Y for after noon?
jnz IsMorning                             ;no, it's before noon
IsAfternoon:
mov dx,OFFSET GoodAfternoonMessage       ;point to the afternoon greeting
jmp DisplayGreeting
IsMorning:
mov dx,OFFSET GoodMorningMessage         ;point to the before noon greeting
DisplayGreeting:
mov  ah,9          &n bsp;                      ;DOS print string function #
int  21h                                  ;display the appropriate greeting
mov  ax,4c00h        &nbs p;                      ;DOS terminate program function #
int  21h                                  ;terminate the program
   main endp
   end main