How to get integer input with assembly

Question

Iam learning assembly and I found out how to get user input with

mov al, 3    ; system call number (sys_read)
xor bl, bl   ; file descriptor 0 (stdin)
mov rcx, buf ; buffer to store input
mov dl, 4    ; Lenght of buffer
int 0x80     ; interrupt

but that actually gets a string right? my question is how do i get a integer value... so if i type 100 how do i get the value 64h so i can add, subtract etc instead of a string with each byte being the ascii representation of the number and then how do i output a value like 64h to the screen so that it shows 100? i dont need code just some guidance

Thanks!

The other way around: integer to string: http://stackoverflow.com/questions/4117422/more-efficient-way-to-output-an-integer-in-pure-assembly — Ciro Santilli OurBigBook.com, May 25 '15 at 06:48

score 7 · Accepted Answer · answered Jul 31 '11 at 22:46

7

Once you have the ASCII representation, you can just build up the result digit by digit, using the fact that the numerals are encoded in order. In pseudo-code, reading from left to right (i.e. starting with the most significant digit):

initialize result to 0
for each digit c, result *= 10; result += (c - '0');
result holds the numeric value of the string

answered Jul 31 '11 at 22:46

Kerrek SB

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+1 The same method applies for other bases (though the `c - '0'` part gets more complicated for bases > 10) – user786653 Jul 31 '11 at 23:04

score 1 · Answer 2 · answered Jul 31 '11 at 22:50

1

Look at binary coded decimals BCD. It can do this a little more efficiently

answered Jul 31 '11 at 22:50

Brett Walker

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How to get integer input with assembly

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