; program to count occurrence of letters $\text{'}$o$\text{'}$ and $\text{'}$r$\text{'}$

$.$MODEL SMALL

$.$STACK $100$h

$.$DATA

txt$\_$len DB $200$

count$1$ DB $0$ ; to store count of $\text{'}$o$\text{'}$

count$2$ DB $0$ ; to store count of $\text{'}$r$\text{'}$

txt DB 'Enter the text of length $200$:$\text{'}$

newline DB $13,10,\text{'}$$$\text{'}$

$.$CODE

MAIN PROC

; initialize Data Segment

MOV AX$,$@DATA

MOV DS$,$AX

; display prompt message

LEA DX$,$txt

MOV AH$,09$h

INT $21$h

; read the text from the user

LEA DX$,$txt

MOV AH$,0$Ah

INT $21$h

; count occurrence of $\text{'}$o$\text{'}$ and $\text{'}$r$\text{'}$

CALL COUNT$\_$OCCURRENCE

; display result

MOV DL$,$count$1$

ADD DL$,30$h

MOV AH$,02$h

INT $21$h

MOV DL$,\text{'}\text{'}$

MOV AH$,02$h

INT $21$h

MOV DL$,$count$2$

ADD DL$,30$h

MOV AH$,02$h

INT $21$h

; display new line

LEA DX$,$newline

MOV AH$,09$h

INT $21$h

; return to DOS

MOV AH$,4$Ch

INT $21$h

MAIN ENDP

COUNT$\_$OCCURRENCE PROC

PUSH SI

MOV CX$,$txt$\_$len

LEA SI$,$txt$+2$

count$\_$o:

CMP $[$SI$],\text{'}$o$\text{'}$

JNE count$\_$r

INC count$1$

count$\_$r:

CMP $[$SI$],\text{'}$r$\text{'}$

JNE next$\_$char

INC count$2$

next$\_$char:

INC SI

LOOP count$\_$o

POP SI

RET

COUNT$\_$OCCURRENCE ENDP

END MAIN