option casemap:none

printf    proto :qword, :VARARG
exit      proto :dword

.data
e_str   db 1 dup (0)

.code
main proc
  xor rcx, rcx
  lea rax, e_str
  cmp byte ptr [rax+rcx],0          ;; Is e_str[0] equal to 0?
  je _isempty                       ;; Yes so goto isEmpty
  jne _notempty                     ;; No, got notEmpty
  jmp _exit                         ;; Neither condition is met, so exit.

  _isempty:
    invoke printf, CSTR("e_str is empty",10)
    lea rax, e_str
    mov byte ptr [rax+0], 's'       ;; Copy a char into e_str[0]
    jmp main                        ;; Test again..

  _notempty:
    invoke printf, CSTR("e_str is NOT empty",10)
    ;; Fall though to exit here..
 _exit:
    xor rsi, rsi
    call exit
    ret
main endp
end