section .data
title db 10, "———————————————————————————————————————————"
    db 10, "ALP to print the addition of N hexadecimal number"
    db 10, "———————————————————————————————————————————"
    db 10, "1.Enter the data "
    db 10, "2.Display the result "
    db 10, "3.Exit "
    db 10, "———————————————————————————————————————————"
    db 10, "Enter your choice "
title_len equ $-title

input1 db 10, "How many numbers you want to enter "
input1_len equ $-input1

input2 db 10, "Enter the 2 digit hex number "
input2_len equ $-input2

output db 10, "Addition of array element is "
output_len equ $-output

wrong db 10, "Wrong choice entered... Please try again"
wrong_len equ $-wrong

section .bss 
    numascii resb 03
    resl resb 01
    resh resb 01
    cnt resb 01
    optionbuff resb 02
    dispbuff resb 04

%macro display 4
    mov rax,%1
    mov rdi,%2
    mov rsi,%3
    mov rdx,%4
    syscall
%endm

section .text
global _start
_start:
menu:
    display 1,1,title,title_len
    display 0,0,optionbuff,02
    cmp byte [optionbuff],"1"
    jne case2
    call procedure
    jmp _start

case2:
    cmp byte [optionbuff],"2"
    jne case3
    display 1,1,output,output_len
    display 1,1,dispbuff,4
    jmp _start

case3:
    cmp byte [optionbuff],"3"
    je exit
    display 1,1,wrong,wrong_len
    jmp _start

procedure:
    display 1,1,input1,input1_len
    display 0,0,numascii,03
    call packnum
    mov [cnt],bl
    xor rcx,rcx
    mov cl,[cnt]

addup:
    push rcx
    display 1,1,input2,input2_len
    display 0,0,numascii,03
    call packnum
    add [resl],bl
    adc byte [resh],0
    pop rcx
    loop addup

    mov bl,[resl]
    mov bh,[resh]
    call disp16_proc
    jmp exit

packnum:
    mov bl,0
    mov rcx,02
    mov rsi,numascii

up1:
    rol bl,04
    mov al,[rsi]
    cmp al,39h
    jbe skip1
    sub al,07h

skip1:
    sub al,30h
    add bl,al
    inc rsi
    loop up1
    ret

disp16_proc:
    mov rcx,04
    mov rdi,dispbuff

dup1:
    rol bx,04
    mov al,bl
    and al,0fh
    cmp al,09
    jbe dskip
    add al,07h

dskip:
    add al,30h
    mov [rdi],al
    inc rdi
    loop dup1
    jmp _start
    ret

exit:
    mov rax,60
    mov rdi,00
    syscall

kodingwindow@kw:~$ nasm -felf64 kw.asm
kodingwindow@kw:~$ ld kw.o && ./a.out

———————————————————————————————————————————
ALP to print the addition of N hexadecimal number
———————————————————————————————————————————
1.Enter the data 
2.Display the result 
3.Exit 
———————————————————————————————————————————
Enter your choice 1

How many numbers you want to enter 02

Enter the 2 digit hex number AF

Enter the 2 digit hex number FF

———————————————————————————————————————————
ALP to print the addition of N hexadecimal number
———————————————————————————————————————————
1.Enter the data 
2.Display the result 
3.Exit 
———————————————————————————————————————————
Enter your choice 2

Addition of array element is 01AE
———————————————————————————————————————————
ALP to print the addition of N hexadecimal number
———————————————————————————————————————————
1.Enter the data 
2.Display the result 
3.Exit 
———————————————————————————————————————————
Enter your choice 3
kodingwindow@kw:~$