CODEWITHSUNDEEP
assembly
user2961971
user2961971

Reputation: 287

Storing an 8 bit unsigned integer

I am having a problem getting my head around of how to store an 8 bit unsigned integer that a user enters from a prompt. The code I have currently is: 

    lea dx, StrPrompt   ;load prompt to display to the user
    mov ah, 9h          ;display string subroutine 
    int 21h             ;interrupt for MS-DOS routine

    mov ah, 1h          ;Read character subroutine (will be stored in al)
    int 21h             ;Interrupt for MS-DOS
    sub al, 30h         ;Translate al from ASCII code to number
    mov num, al         ;Copy number to num (al will be overwritten later)

    lea dx, StrMsg      ;display the results to the user
    mov ah, 9h 
    int 21h

    mov al, num         ;move the n value to the al
    mov dl, al          ;display the number
    add dl, 30h         ;add 30h to the ASCII table
    mov ah, 2h          ;store interrupt code
    int 21h             ;interrupt for MS-DOS routine

The problem right now is that each time I run this it will only allow me to enter a single integer number like 1, 2, 3, etc. I am unable to enter in a double or triple digit number like 20 or 255. How do I go about this?

Upvotes: -1

Views: 1189

Answers (1)

zx485
zx485

Reputation: 29022

mov ah, 1h          ;Read character subroutine (will be stored in al)

Here it says that it reads exactly one char. 20 or 255 consist of two and respectively 3 chars. If you want to read in more than one char you'd have to put this in a loop or use the other API/INT-call from the comment above.

The loop variant may look like this - the loop unrolled for up to three chars

.data
  num1 db 0
  num2 db 0
  num3 db 0
  numAll dw 0
.code
  [...]
mov ah, 1h          ;Read character subroutine (will be stored in al)
int 21h             ;Interrupt for MS-DOS
sub al, 30h         ;Translate al from ASCII code to number
mov num1, al         ;Copy number to num (al will be overwritten later)

mov ah, 1h          ;Read character subroutine (will be stored in al)
int 21h             ;Interrupt for MS-DOS
cmp al,13           ;check for return
je exit1            ;if return, do not ask further and assume one digit
sub al, 30h         ;Translate al from ASCII code to number
mov num2, al         ;Copy number to num (al will be overwritten later)

mov ah, 1h          ;Read character subroutine (will be stored in al)
int 21h             ;Interrupt for MS-DOS
cmp al,13           ;check for return
je exit2            ;if return, do not ask further and assume two digits
sub al, 30h         ;Translate al from ASCII code to number
mov num3, al        ;Copy number to num2 (al will be overwritten later)
[...]
exit2:
[...]
exit1:

Upvotes: 1

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