String Operations

Working with Strings

In assembly, strings are just sequences of bytes in memory. You manipulate them by loading and storing individual bytes.

Reading Bytes from Memory

Use the BYTE size specifier to access individual bytes:

movzx rax, BYTE [rsi]     ; load one byte, zero-extend to 64 bits
mov BYTE [rdi], al         ; store low byte of rax

movzx (move with zero-extension) loads a small value and fills the upper bits with zeros.

Iterating Over a String

To process each character of a null-terminated string:

	lea rsi, [mystring]
loop:
	movzx rax, BYTE [rsi]
	cmp rax, 0            ; check for null terminator
	je done
	; ... process character in rax ...
	inc rsi               ; advance to next character
	jmp loop
done:

Computing String Length

Count characters until you hit a null byte (0) or a known terminator.

Your Task

Write a program that computes the length of the string "Hello" (which is 5 characters) and prints it as a digit followed by a newline.

The string is stored in the data section with a null terminator. Loop through it, counting characters until you reach the null byte.

Print: "5\n"