 
data SEGMENT; Define string
hello DB 'Hello World$'
hello2 DB 'See you!$'
 newline DB 13,10,'$'; define a newline string
data ENDS
code SEGMENT
    ASSUME CS:CODE,DS:DATA
start:
    MOV AX,data                  
    MOV DS,AX 
    MOV AH, 01H; Set parameter 01H for AH
 INT 21h INT 21h; Execute the 01H function set in AH: Enter a value into AL
 SUB AL,48; Subtract 48 from the obtained value, and the value of '0' in ASCII is 48 
 MOV CL, AL; Assign AL to CL 
 MOV AH,09H; Set parameter 09H for AH
 L5: LEA DX, newline; Point DX to the string newline 
 INT 21h Execute the function of No. 09H in AH and output the string newline 
 LEA DX, hello; Point DX to the string hello 
 INT 21h INT 21h; execute the function of No. 09H in AH, and output the string hello
 LOOP L5; CX minus one, judge whether CX is zero, if CX is not zero, continue the cycle 
 MOV AX, 4C00H; Set parameter 4C00H for AX 
 INT 21h INT 21h; execute the 4C00H function in AH to end the program
code ENDS
END start

created 3 years ago

Assembly Online Compiler

Write, Run & Share Assembly code online using OneCompiler's Assembly online compiler for free. It's one of the robust, feature-rich online compilers for Assembly language. Getting started with the OneCompiler's Assembly compiler is simple and pretty fast. The editor shows sample boilerplate code when you choose language as Assembly and start coding.

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