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: stackoverflow.com/questions/4117422/… — Ciro Santilli OurBigBook.com
– Ciro Santilli OurBigBook.com, Commented May 25, 2015 at 6:48

Kerrek SB · Accepted Answer · 2011-07-31 22:46:51Z

8

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, 2011 at 22:46

Kerrek SB

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1 Comment

user786653 Over a year ago

+1 The same method applies for other bases (though the c - '0' part gets more complicated for bases > 10)

Brett Walker · Accepted Answer · 2011-07-31 22:50:31Z

1

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

answered Jul 31, 2011 at 22:50

Brett Walker

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