Question

Write an assembly procedure Find to return the index of the first occurrence of a character ch in a string str.
If ch is not found in str the return value should be -1.

Input parameters:

None.

Preconditions: 

The base address of str is stored in ecx. 

str is ‘\0’ terminated.

ch is strored in bl.

Return value:

The return value should be stored in eax.

Run and test your procedure using the following driver program:

.386

.model flat, stdcall

option casemap : none

.data

MyStr byte "Assembly Lab 8: Procedures", 0

MyCH  byte ":"

.code

;write your procedure here.

start:

lea ecx, MyStr

mov bl, MyCH

call Find
ret
end start

Answer 1

DATA SEGMENT MSG1 DB "ENTER THE STRING : $" MSG2 DB "NO OF OCCURANCES OF N : $" NEWLINE DB 10,13,'$' STR1 DB 80 DUP('$') bl DB ch CNT DB 0 DATA ENDS CODE SEGMENT ASSUME DS:DATA,CS:CODE START : MOV AX,DATA MOV DS,AX MOV AH,09H LEA DX,MSG1 INT 21H MOV AH,0AH LEA DX,STR1 INT 21H MOV AH,09H LEA DX,NEWLINE INT 21H LEA SI,STR1+1 MOV CL,BYTE PTR[SI] MOV CH,00H #ITERATING THE STRING AND FINDING THE FIRST OCCURRENCE OF bl L1 : INC SI CMP BYTE PTR[SI],bl JNZ L2 INC CNT MOV EAX,SI L2 : LOOP L1 ADD CNT,'0' MOV AH,09H LEA DX,MSG2 INT 21H JNZ CNT MOV AH,02H MOV DH,00H MOV DL,EAX INT 21H MOV AH,4CH INT 21H CODE ENDS END START