Slide 3.5: Filename extensions and comments

Filename Extensions and Comments

The following slides of this week explain the sample program, , in detail.

Filename Extensions
A filename extension indicates the kind of data stored in the file.

Extension	Comments
`.ASM`	Assembly language source file (uncompiled)
`.BAT`	Batch file, ASCII file of DOS commands, [EXECUTABLE]
`.EXE`	Executable file (program) (binary) [EXECUTABLE]
`.LST`	List file
`.MAP`	A text file that contains information about the segments contained in a program being linked
`.OBJ`	Object file
`.PDB`	The program database file with which the debugger is then able to display the program’s source code and provide supplemental information about the program.

TITLE Directive
A directive is a command that is recognized and acted upon by the assembler. It is not related to the Intel instruction set. Directives are used for defining logical segments, choosing a memory model, defining variables, creating procedures, and so on.

    TITLE  Read and Subtract     (ReadSub.asm)

The directive marks the entire line as a comment.

Comments
Comments can be specified in two ways:

Single-line comments, beginning with a semicolon character ().
```
   call   WriteString              ; print prompt1
```
Block comments, beginning with the directive and a user specified symbol such as ().
```
   COMMENT  !
        This program reads and subtracts 32-bit integers.
   !
```

ReadSub.asm

COMMENT!
*
* This program reads and subtracts 32-bit hexadecimal integer from 50000h.
*
!

INCLUDE Irvine32.inc

.data
  prompt1  BYTE   0Dh, 0Ah, "Calculate an Arithmetic Expression of 50000h - Y:",
                  0Dh, 0Ah, 0
  prompt2  BYTE   "Enter the value of operand Y:   ", 0
  prompt3  BYTE   0Dh, 0Ah, "The result is  ", 0
  X        DWORD  50000h
  Y        DWORD  ?
  result   DWORD  ?
 
.code
main PROC
  mov    edx, OFFSET prompt1
  call   WriteString            ; print prompt1

  mov    edx, OFFSET prompt2
  call   WriteString            ; print prompt2

  call   ReadHex
  mov    Y, eax                 ; Y   = eax (the input)
  mov    eax, X                 ; eax = X (50000h)

  ; calculate 50000h – Y
  sub    eax, Y                 ; eax    = X (50000h) – Y (the input)
  mov    result, eax            ; result = eax (X – Y)

  mov    edx, OFFSET prompt3
  call   WriteString            ; print prompt3

  call   WriteHex               ; print eax (result)
  exit

main ENDP
END  main

An Execution Example


 Calculate an Arithmetic Expression of 50000h – Y:
 Enter the value of operand Y:  4000 

 The result is  0004C000

^†The white italic text with a navy background color is entered by users.