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!

Answer 1

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