SUBROUTINE TO CONVERT CHARACTERS IN MEMORY TO A DECIMAL VALUE

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                              AUTHOR:  ANUEBUNWA VICTOR OGECHUKWU                                            

               SUBROUTINE TO CONVERT CHARACTERS IN MEMORY TO A DECIMAL VALUE                            
 Subroutine CHAR2INTR converts characters in memory to a decimal value and stores it in AX.             
 i.e '1','2','3','4' in memory ==> 1234 in AX                                                          
 .......................................................................HOW TO USE......................................................................
 (1) Load the starting address of the memory into SI register.                                          
 (2) Call CHAR2INTR.                                                                                                          ***********************************************************************************************************

;         SAMPLE PROGRAM
.MODEL SMALL
.STACK
.DATA
    AVON DB ?
.CODE
START:        MOV AX, @DATA
            MOV DS, AX
           
            MOV AH, 3FH
            LEA DX, AVON
            INT 21H                    ;Reads characters into memory, using AVON as a starting address
           
            LEA SI, AVON            ;Loads starting address into SI
            CALL CHAR2INTR            ;Calls CHAR2INTR to convert characters to a decimal value
            MOV DX, AX                ;Puts decimal value into DX
            MOV AH, 02H
            INT 21H                    ;Displays character whose ASCII code equals the decimal value
           
            MOV AH, 4CH
            INT 21H

;Subroutine CHAR2INTR
CHAR2INTR PROC
            PUSH BX
            PUSH CX
            PUSH DX
            PUSH SI
            PUSHF
           
            MOV AX, 0000H
            MOV CX, 0000H
CLOOP1:        MOV AX, [SI]            ;Loads character currently pointed to into AX
            CMP AL, '9'
            JNLE XCLOOP1            ;Exits loop if character is not less or equal to '9'
            CMP AL, '0'
            JNGE XCLOOP1            ;Exits loop if character is not greater or equal to '0'
            INC CL                    ;Else, Keeps count of the number of characters being processed
            INC SI                    ;Moves pointer to the next character
            SUB AL, 30H                ;Converts character to digit
            PUSH AX                    ;Pushes digit to stack
            JMP CLOOP1                ;continues loop

XCLOOP1:    MOV BX, 0001H
            MOV DX, 0000H
CLOOP2:        CMP CL, 0                ;Checks number of characters processed
            JE XCLOOP2                ;Exits loop if no character was processed i.e CL = 0
            POP AX                    ;Else, pops digit from stack to AX
            MUL BL                    ;Multiplies digit with it's PLACEMENT-VALUE. RECALL: unit = 1, tens = 10, hundreds = 100 ...
            ADD DX, AX                ;Adds (digit * PLACEMENT-VALUE)s together. RECALL: 234 = (4 * 1) + (3 * 10) + (2 * 100) where 1,10,100 represent their PLACEMENT-VALUES
            MOV AX, 10               
            MUL BL                    ;Multiplies current PLACEMENT-VALUE by 10 to advance to the next PLACEMENT-VALUE.
            XCHG AX, BX                ;Puts result from multiplication back to BX
            DEC CX                    ;Reduces count
            JMP CLOOP2                ;Loop continues
           
XCLOOP2:    MOV AX, DX                ;Moves converted value to AX
           
            POPF
            POP SI
            POP DX
            POP CX
            POP BX
            RET
CHAR2INTR ENDP
;End of Subroutine CHAR2INTR

END START

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