.MODEL SMALL
.STACK 100h
.DATA

    msg db "Enter string:", 13, 10, "$"
    buffer db 100, ?, 100 dup('$')
    endline db 13, 10, "$"

    inf db "in.txt", 0
    outf db "out.txt", 0

.CODE

    MOV ax, @data
    MOV ds, ax

    ; print string
    MOV dx, offset msg
    MOV ah, 09h
    INT 21h

    ; scan string
    MOV dx, offset buffer
    MOV ah, 0Ah
    INT 21h

    ; print endline
    MOV dx, offset endline
    MOV ah, 09h
    INT 21h

    ; print string
    MOV dx, offset buffer
    ADD dx, 2
    MOV bx, dx
    MOV cl, [bx-1]
    MOV ch, 0
    ADD bx, cx
    MOV byte ptr [bx], '$'
    MOV ah, 09h
    INT 21h

    ; exit program
    MOV ax, 4C00h
    INT 21h

END