[ASM x86] - Simple reading program.

.model small
.stack 100h
SETPOS macro X,Y
  MOV AH, 2H
  MOV DL, Y
  MOV DH, X
  INT 10H
ENDM
PRT macro STR
  MOV AH, 9H
  MOV DX, OFFSET STR
  INT 21H
ENDM
STRAPPEND macro CH
  MOV CL, BUFFLEN
  MOV DL, CH
  CALL SUBSTR
ENDM


        .data
mip DB 'Hallo werld!$'
BUFFMAX DB 40
BUFFLEN DB 1
app DB 40 DUP(?),'$'
        .code
MOV AX, @DATA
MOV DS, AX
MOV DI, OFFSET mip
INC DI
MOV BYTE PTR[DI], 'e'
GETINP:
  MOV AH, 1H
  INT 21H
  CMP AL, 0DH
  JE INPEND
  STRAPPEND AL
  JMP GETINP
INPEND:
  CMP BUFFLEN, 41
  JL EXITP
  STRAPPEND '$'
EXITP:
  PRT app
  MOV AH, 4CH
  INT 21H

;------- CALL STATEMENTS --
SUBSTR PROC
 ; TAKES CL AS CH INDEX, AND DL AS CHAR
  LEA DI, app
  MOV BL, 0
  SUBNXT:
    INC DI
    INC BL
    CMP CL, BL
    JE SUBDONE
    JMP SUBNXT
  SUBDONE:
    MOV BUFFLEN, CL
    INC BUFFLEN
    MOV BYTE PTR[DI], DL
  RET
SUBSTR ENDP
END