asm3

;a factorial program with a key piece missing.
; can you find: how to print a message to the screen
;how to "declare a variable"
;where to declare a variable
;how to read in a char and convert to a digit
;how does multiply work? (mul)
;can you find the loop?
;how do you increment a value in assembly?
;exercise: write the program in c and compare...
;what piece is missing?
.model small
        .stack 100h
        .data
        factval dw ?
       fact dw 1
        prompt db 'enter a value between 1 and 9' ,0ah,0dh,'$'
        input db ' was input*',10,13,'$'
output db ' is the answer',0ah,0dh,'$'
        .code
INCLUDE decout.asm
factorial:
        mov ax, @data
        mov ds,ax

   &nbs p;    mov ah,9                        ;put message on screen
        mov dx, offset prompt
        int 21h

        mov ah,1                        ; ;get int value
        int 21h
        and al, 0Fh                     ;preserve digit part
        xor ah,ah
        mov cx,ax                   ;store this digit in CX
        mov ax,1
looptop:
        mul [fact]
        inc [fact]
        loop looptop
        mov [factval],ax                ;save factorial
mov dx, offset input
mov ah,9
int 21h         call dec_out
        mov dx, offset output
        mov ah,9
        int 21h
        mov ah,4ch              ;terminate sequence
        int 21h
        END facto rial
        END