 ;; Brandon Quan
	;; ID: TC56450
	;; This program asks a user for input of a string with 8 charaters
	;; then it ask the user for the number of letters that will be cut off from the string
	section .rodata
length:	equ 8 		;Length of string
num: equ 3

	section .data
prompt1: db    "Enter Text:", 10
len_p1:	equ   $ - prompt1
	
prompt2: db  "Enter the number of charters to cut off:", 10
len_p2:	equ  $ - prompt2

prompt3: db "This is what you entered:", 10
len_p3:	equ $ - prompt3

prompt4: db 10,"Here is your text edited:", 10
len_p4:	equ $ - prompt4

	section .bss
input:	 resb length
userinput:	 resb num
output:	 resb length

	section .text

	global main
main:
	mov rax, 1
	mov rdi, 1
	mov rsi, prompt1
	mov rdx, len_p1
	syscall            	;Display first prompt

	mov rax, 0
	mov rdi, 0
	mov rsi, input
	mov rdx, length
	syscall 		;User input
	
	mov rax, 1
	mov rdi, 1
	mov rsi, prompt2
	mov rdx, len_p2
	syscall ;Displays second prompt
	
	mov rax, 0
	mov rdi, 0
	mov rsi, input
	mov rdx, num
	syscall ;User input

	mov rax, 1
	mov rdi, 1
	mov rsi, prompt4
	mov rdx, len_p4
	syscall 		;Displays entered text

	mov rax, 1
	mov rdi, 1
	mov rsi, input
	mov rdx, length
	syscall

				;Edit the text
	mov bl, [input]
	sub bl, 48
	

	mov rax, 1
	mov rdi, 1
	mov rsi, input
	add rsi, rbx
	syscall			;display output

				;Exit
	mov rax, 60
	xor rdi, rdi
	syscall

created 3 years ago

Assembly Online Compiler

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About Assembly

Assembly language(asm) is a low-level programming language, where the language instructions will be more similar to machine code instructions.

Every assembler may have it's own assembly language designed for a specific computers or an operating system.

Assembly language requires less execution time and memory. It is more helful for direct hardware manipulation, real-time critical applications. It is used in device drivers, low-level embedded systems etc.

Syntax help

Assembly language usually consists of three sections,

Data section

To initialize variables and constants, buffer size these values doesn't change at runtime.
bss section

To declare variables
text section

_start specifies the starting of this section where the actually code is written.

Variables

There are various define directives to allocate space for variables for both initialized and uninitialized data.

1. To allocate storage space to Initialized data

Syntax

variable-name    define-directive    initial-value

Define Directive	Description	Allocated Space
DB	Define Byte	1 byte
DW	Define Word	2 bytes
DD	Define Doubleword	4 bytes
DQ	Define Quadword	8 bytes
DT	Define Ten Bytes	10 bytes

2. To allocate storage space to un-initialized data

Define Directive	Description
RESB	Reserve a Byte
RESW	Reserve a Word
RESD	Reserve a Doubleword
RESQ	Reserve a Quadword
REST	Reserve a Ten Bytes

Constants

Constants can be defined using

1. equ

To define numeric constants

CONSTANT_NAME EQU regular-exp or value

2. %assign

To define numeric constants.

%assign constant_name value

3. %define

To define numeric or string constants.

%define constant_name value

Loops

Loops are used to iterate a set of statements for a specific number of times.

mov ECX,n
L1:
;<loop body>
loop L1

where n specifies the no of times loops should iterate.

Procedures

Procedure is a sub-routine which contains set of statements. Usually procedures are written when multiple calls are required to same set of statements which increases re-usuability and modularity.

procedure_name:
   ;procedure body
   ret