NASM program to echo a character string

section .data
msg: db "Enter character string: "
len: equ $-msg
msg1: db "Result: "
len1: equ $-msg1

section .bss
var: resb 1
leng: resb 1

section .text
global _start
_start:

mov eax,4
mov ebx,1
mov ecx,msg
mov edx,len
int 80h

mov eax,3
mov ebx,0
mov ecx,var
mov edx,leng
int 80h

mov eax,4
mov ebx,1
mov ecx,msg1
mov edx,len1
int 80h

mov eax,4
mov ebx,1
mov ecx,var
mov edx,leng
int 80h

mov eax,1
mov ebx,1
int 80h

NASM Program to add 2 numbers

section .data
msg1 db "Enter a number: "
len1 equ $-msg1
msg2 db "Enter the second number: "
len2 equ $-msg2
msg3 db "Sum = "
len3 equ $-msg3

section .bss
num1 resb 2
num2 resb 2
res resb 1
r1 resb 1
section .txt
global _start
_start:
mov eax, 4
mov ebx, 1
mov ecx, msg1
mov edx, len1
int 80h

mov eax, 3
mov ebx, 0
mov ecx, num1
mov edx, 2
int 80h

mov eax, 4
mov ebx, 1
mov ecx, msg2
mov edx, len2
int 80h

mov eax, 3
mov ebx, 0
mov ecx, num2
mov edx, 2
int 80h

mov eax, [num1]
sub eax, 30h
mov ebx, [num2]
sub ebx, 30h
add eax, ebx
daa
mov [res], eax

mov eax, 4
mov ebx, 1
mov ecx, msg3
mov edx, len3
int 80h

mov al, [res]
and ax, 00f0h
shr ax, 4
add ax, 30h
mov [r1], ax

mov ecx, r1
mov edx, 1
mov eax, 4
mov ebx, 1
int 80h

mov al, [res]
and ax, 000fh
add ax, 30h
mov [r1], ax

mov ecx, r1
mov edx, 1
mov eax, 4
mov ebx, 1
int 80h

mov eax, 1
mov ebx, 0
int 80h