org 100h

;output task

mov ah, 9h

mov dx, str1

int 21h

;output task

mov ah,9h

mov dx, str2

int 21h

;output task

mov ah,9h

mov dx, str3

int 21h

;input string

mov ah,0Ah

mov dx, my_str

int 21h

;new line break

mov ah,9h

mov dx, new_line

int 21h

;swap 4 and 6

mov bp, my_str+2 ;address 1st

mov cl,[bp+3] ;4th element

mov ch, [bp+5] ;6th element

xchg ch,cl ;swap

mov [bp+5],ch

mov [bp+3],cl

;9rd - 1th

mov ch, [bp+8]

sub ch, [bp]

;3rd - (9rd - 1th)

mov cl, [bp+2]

sub cl, ch

mov [bp+4], cl

;output result

mov ah,9h

mov dx, bp

int 21h

;waiting to press

mov ah, 8h

int 21h

ret

str1 db "This program swaps the 4s and 6s characters of the string. ",$0d,$0a, "$"

str2 db "Performs arithmetic operations: S3 - (S9 - S1). Result is written to S5. ",$0d,$0a, "$"

str3 db "Input string (max. 10 elements)", $0d, $0a, "$"

my_str db 11,0,11 dup('$')

new_line db $0d, $0A, "$"