substring.asm

DATA SEGMENT
    STR DB 'AXYBCSDEF$'
    SUBSTR DB 'BCS$'
    LEN1 DB 0
    LEN2 DB 0
    MSG1 DB 10,13,'STRING IS : $'
    MSG2 DB 10,13,'SUBSTRING IS : $'
    MSG3 DB 10,13,'SUBSTRING IS FOUND AT POSITION : $'
    POS DB -1
    RTN DB '-1$'
DATA ENDS

DISPLAY MACRO MSG
    MOV AH,9
    LEA DX,MSG
    INT 21H
ENDM  

CODE SEGMENT
    ASSUME CS:CODE,DS:DATA
    START:
    MOV AX,DATA
    MOV DS,AX
    DISPLAY MSG1
    DISPLAY STR
    DISPLAY MSG2
    DISPLAY SUBSTR
    LEA SI,STR
    
    NXT1:
    CMP [SI],'$'
    JE DONE1
    INC LEN1
    INC SI
    JMP NXT1
    
    DONE1:
    LEA DI,SUBSTR

    NXT2:
    CMP [DI],'$'
    JE DONE2
    INC LEN2
    INC DI
    JMP NXT2
    
    DONE2:
    DISPLAY MSG3
    LEA SI,STR
    MOV AL,LEN1
    SUB AL,LEN2
    MOV CL,AL
    MOV CH,0
    
    FIRST:
    INC POS
    MOV AL,[SI]
    CMP AL,SUBSTR[0]
    JE CMPR
    INC SI
    LOOP FIRST

    CMPR: 
    INC SI
    MOV AL,[SI]
    CMP AL,SUBSTR[1]
    JNE NOTEQUAL
    INC SI
    MOV AL,[SI]
    CMP AL,SUBSTR[2]
    JE EQUAL

    NOTEQUAL:
    MOV POS,-1
    DISPLAY RTN
    JMP EXIT
    
    EQUAL:
    MOV DL,POS
    ADD DL,30H
    MOV AH,2
    INT 21H

    EXIT: 
    MOV AH,4CH
    INT 21H
CODE ENDS
END START