countDownLoop.asm

; Assembly code to loop and print reducing numbers (count down)

section .data
message db "Count Down: ", 10 ; message  countdown
messageLen equ $-message; length of message
newLine db 10 ; newline like endl in C++

section .bss 
number resb 1 ; number variable 1  byte long
section .text
global _start
_start:
call printMessage ; call print message function
mov rax,9 ;Move integer 9 into rax register
loopNum: ; loop function
  push rax ; push rax value on the stack
  add rax,'0' ; convert integer in rax into ascii to print
   mov [number],rax ;put the value in rax in the variable number 
	call print ; call print function
  pop rax ; get rax back from the stack
	dec rax ;decrement the value of rax by 1
   cmp rax,0 ; compare rax with 0
	jne loopNum ;if not equal to zero go to loopNum
 call end ; call end function
 printMessage:
   mov eax,4 ; system call for print to screen
   mov ebx, 1; standard out
   mov ecx, message ; count down message
    mov edx, messageLen ; length of message
   int 80h ; interrupt
   ret
 print:
   mov eax,4 ; system call for print to screen
   mov ebx, 1 ; standard out
   mov ecx,  number ; number variable
    mov edx, 1 ; size of number
   int 80h ; interrupt
   mov eax,4 ; system call for print to screen
   mov ebx, 1 ; standard out
   mov ecx,  newLine; new line like endl C++
    mov edx, 1 ; size of number
   int 80h ; interrupt
   ret
 end:
 mov eax,1 ; system call for exit
 mov ebx,0 ; return value
 int 80h ; interrupt
	ret