xseg
kstr: ds 30

cseg at 0
jmp _start
istr: db "This programmator",0

_start:
// initializing

mov R0, #0 // R0 is used for input str offset counter

mov dptr, #kstr // Saving 16-bit address of output str into DPTR
mov R2, dpl // And saving dptr in R2 and R3
mov R3, dph

__loop:
mov DPTR, #istr
mov a, R0
movc a, @a+DPTR

jz __end // null-terminator? end

mov dpl, R2 // Restoring sabed address in DPTR
mov dph, R3
movx @DPTR, a

cjne a, #'r', __notr // if not 'r', skipping inserting of letter

inc DPTR // next letter
mov a, #' ' // will be a ' '
movx @DPTR, a

__notr:
inc DPTR // Inc DPTR anyway
mov R2, dpl // and save
mov R3, dph

inc R0 // Int input string pointer

jmp __loop

__end:

end