8086 basic mathematic expression-CodePudding

I have to do an operation like this in 8086

((x*y)-c) 1

I wrote this code:

.stack
.data
A dw 180
B db 4  
C dw 300 


.code
start:
    
    MOV AX, 00h
    MOV AX, A
    MUL B
    SUB AX, C
    DEC AX
    int 21h 
end start

This code works but I don't think does the expression I wanted...

Where am I wrong?

CodePudding user response：

This code works but I don't think does the expression I wanted...

((x * y) - c)   1

The calculation is almost correct. Just the DEC AX should become INC AX so it matches the expression where you add 1 in the end:

Looking at my teacher's example he always uses int 21h at the end of his code

I'm sure your teacher's code will have something like mov ah, 00h or mov ax, 4C00h directly above that line. It's meant to terminate the program and return to DOS.

This is the code that additionally shows the result of the calculation on the screen. The program waits for a keyboard key before it terminates giving you the opportunity to actually see the outcome.

start:
    mov  ax, A
    mul  B
    sub  ax, C
    inc  ax         ; -> AX == 421

    mov  bx, 10
    xor  cx, cx
Divide:
    xor  dx, dx     ; Setup for division DX:AX / BX
    div  bx         ; -> Quotient AX, Remainder DX=[0,9]
    push dx         ; (1)
    inc  cx
    test ax, ax
    jnz  Divide
Show:
    pop  dx         ; (1)
    add  dl,"0"     ; [0,9] -> ["0","9"]
    mov  ah, 02h    ; DOS.DisplayCharacter
    int  21h        ; -> AL
    dec  cx
    jnz  Show

    mov  ah, 01h    ; DOS.GetKey
    int  21h        ; -> AL

    mov  ax, 4C00h  ; DOS.Terminate
    int  21h 
end start