Filename Extensions and Comments

The following slides of this week explain the sample program, ReadSub.asm, 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 TITLE directive marks the entire line as a comment.

Comments
Comments can be specified in two ways:
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.




      “I’m not afraid of death;    
      I just don’t want to be there when it happens.”    
      — Woody Allen