Intro to Assembly Language: Lecture Notes | CISC 3310

NASM Coding: Constants and String Length

We can declare constant values in several ways in NASM:

Using the
```
equ
```
pseudo-instruction:
```
name equ expression
```
Example:
```
msg db "Hello", 10
len equ $ - msg
```
Explanation: we set
```
msg
```
to be the string
```
"Hello\n"
```
. Then, we set
```
len
```
to be the size of the string
```
msg
```
, which is
```
6
```
.
Fun fact: the expression
```
$ - msg
```
is actually address subtraction: we subtract the start address of
```
msg
```
from the most recent address (which is stored at
```
$
```
), which happens to be the end address of
```
msg
```
after running the previous instruction. This results in the length of the string
```
msg
```
.