Question

I'm working in assembly using nasm, and need to create a program that performs simple calculations. The prompt is below:

Write a program that contains 4 procedures:

ADD

SUBTRACT

MULTIPLY

DIVIDE

Read expressions from the user, such as:

1 + 2

4 - 3

2 * 3

4 / 2

.

Execute every expression by calling the proper procedure.

The end of user input is a period: .

The output for the above code should be:

1 + 2 = 3

4 - 3 = 1

2 * 3 = 6

4 / 2 = 2

Answer 1

=============== nasm assembly code for above function is=========================

;;;; declaring the frequently used number
SYS_EXIT equ 1
SYS_READ equ 3
SYS_WRITE equ 4
STDIN equ 0
STDOUT equ 1

segment .data
;;; declaring the messages and their length
msg1 db "Enter a digit: ", 0xA,0xD
len1 equ $- msg1

msg2 db "Please enter a second digit:", 0xA,0xD
len2 equ $- msg2

msg3 db "The sum is: "
len3 equ $- msg3
  
msg4 db "The subtraction is :"
len4 equ $- msg4
  
msg5 db "The multiply is:"
len5 equ $- msg5
  
msg6 db "The division is:"
len6 equ $- msg6

segment .bss

num1 resb 2 ;holds 2 byte number
num2 resb 2 ;same as above
res resb 1 ;holds one byte number

section   .text
global _start ;global start for gcc
  
_start: ;entry point for the linker

;;;;;;;;;; addition
;;;;; printing to enter a number
mov eax, SYS_WRITE   
mov ebx, STDOUT   
mov ecx, msg1   
mov edx, len1
int 0x80
;;;;;;;;; reading first number
mov eax, SYS_READ
mov ebx, STDIN
mov ecx, num1
mov edx, 2
int 0x80
;;;;;;;; printing message to enter second number
mov eax, SYS_WRITE
mov ebx, STDOUT   
mov ecx, msg2
mov edx, len2   
int 0x80
;;;;;;;;;;reading second number
mov eax, SYS_READ
mov ebx, STDIN
mov ecx, num2
mov edx, 2
int 0x80
;;;;;;;;;;writing about result
mov eax, SYS_WRITE   
mov ebx, STDOUT   
mov ecx, msg3
mov edx, len3   
int 0x80

;;;;;;;; calculation from here
mov eax, [num1]
sub eax, '0'
mov ebx, [num2]
sub ebx, '0'
add eax, ebx
add eax, '0'
mov [res], eax
mov eax, SYS_WRITE
mov ebx, STDOUT
mov ecx, res   
mov edx, 1
int 0x80

;;;;;;;;;;;;;;; subtraction ;;;;;;;;;;;;;;;;;;;;;;;;;;;
mov eax, SYS_WRITE   
mov ebx, STDOUT   
mov ecx, msg1   
mov edx, len1
int 0x80
mov eax, SYS_READ
mov ebx, STDIN
mov ecx, num1
mov edx, 2
int 0x80
mov eax, SYS_WRITE
mov ebx, STDOUT   
mov ecx, msg2
mov edx, len2   
int 0x80
mov eax, SYS_READ
mov ebx, STDIN
mov ecx, num2
mov edx, 2
int 0x80
mov eax, SYS_WRITE   
mov ebx, STDOUT   
mov ecx, msg4   
mov edx, len4   
int 0x80
mov eax, [num1]
sub eax, '0'
mov ebx, [num2]
sub ebx, '0'
sub eax, ebx
add eax, '0'
mov [res], eax
mov eax, SYS_WRITE
mov ebx, STDOUT
mov ecx, res   
mov edx, 1
int 0x80
;;;;;;;;;;;;;;;;;;;;;;;;;;;; multiplication ;;;;;;;;;;;;;;;;;;;;;

mov eax, SYS_WRITE   
mov ebx, STDOUT   
mov ecx, msg1   
mov edx, len1
int 0x80
mov eax, SYS_READ
mov ebx, STDIN
mov ecx, num1
mov edx, 2
int 0x80
mov eax, SYS_WRITE
mov ebx, STDOUT   
mov ecx, msg2
mov edx, len2   
int 0x80
mov eax, SYS_READ
mov ebx, STDIN
mov ecx, num2
mov edx, 2
int 0x80
mov eax, SYS_WRITE   
mov ebx, STDOUT   
mov ecx, msg5
mov edx, len5   
int 0x80
mov al, [num1]
sub al, '0'
mov bl, [num2]
sub bl, '0'
mul bl
add al, '0'
mov [res], al
mov eax, SYS_WRITE
mov ebx, STDOUT
mov ecx, res   
mov edx, 1
int 0x80

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; division ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

mov eax, SYS_WRITE   
mov ebx, STDOUT   
mov ecx, msg1   
mov edx, len1
int 0x80
mov eax, SYS_READ
mov ebx, STDIN
mov ecx, num1
mov edx, 2
int 0x80
mov eax, SYS_WRITE
mov ebx, STDOUT   
mov ecx, msg2
mov edx, len2   
int 0x80
mov eax, SYS_READ
mov ebx, STDIN
mov ecx, num2
mov edx, 2
int 0x80
mov eax, SYS_WRITE   
mov ebx, STDOUT   
mov ecx, msg6
mov edx, len6   
int 0x80
mov ax, [num1]
sub ax, '0'
mov bl, [num2]
sub bl, '0'
div bl
add ax, '0'
mov [res], ax
mov eax, SYS_WRITE
mov ebx, STDOUT
mov ecx, res   
mov edx, 1
int 0x80
exit:

mov eax, SYS_EXIT   
xor ebx, ebx
int 0x80

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