'===========================================================================
' Subject: ASSEMBLY AND BASIC                 Date: Unknown Date (00:00)   
'  Author: Matt Hart                          Code: ASM, QB, PDS           
'  Origin: ASSEMBLY,AND,BASIC               Packet: ASMCODE.ABC
'===========================================================================
; ASCII.ASM by Matt Hart
; Returns the ASCII code of a string
; like ASC does BUT will return a -1 if
; the string is NULL rather than bombing out with
; an ILLEGAL FUNCTION CALL.
;
.Model Medium, BASIC
.Code
;
Ascii PROC USES SI, Strg:Word
    MOV     BX,Strg         ; Pointer to descriptor
    MOV     CX,[BX]         ; Length
    CMP     CX,0            ; Is the string null?
    JE      NullString      ; Yes - jump to NullString
    MOV     SI,[BX+2]       ; Address of the string into SI
    XOR     AX,AX           ; Clear AX to receive the character
    MOV     AL,[SI]         ; First character of the string
    JMP     Ending          ; Back to BASIC
NullString:
    MOV     AX,0FFFFh       ; Return a -1 to the function
Ending:
    RET                     ; Back to BASIC
Ascii ENDP
    END

C:\>masm ascii.asm
     or
C:\>ml /c ascii.asm

'TEST.BAS
DEFINT A-Z
DECLARE FUNCTION Ascii(Strg$)
PRINT Ascii(COMMAND$)

C:\>bc test;
C:\>link test+ascii,,,brun45;
C:\>test A