programming-for-dummies

278
Adding Comments to Source Code
SECTION .text
global main
main:
mov eax,4;
write system call
mov ebx,1
mov ecx,msg
mov edx,len
int 0x80
mov eax,1 system call
mov ebx,0
int 0x80
You could replace the preceding assembly language commands with a
shorter, more descriptive high-level language command like this:
PRINT “It’s alive!”
Such self-documenting code helps explain what a single line of code does,
but doesn’t necessarily tell you how the entire program works as a whole or
what problem the program even solves.
Rather than rely on “self-explanatory” language commands, programmers
started adding explanations directly into the source code itself by using
comments.
A comment is nothing more than text, embedded in the source code. To keep
the compiler from thinking a comment is an actual command, every comment
needs a special symbol in front of the comment, such as
REM This is a comment in BASIC
‘ This is another comment in BASIC
// This is a comment in C++ and Java
# This is a comment in Perl and Python
; This is a comment in LISP and assembly language
Comments allow you to write short explanations, directly in the source
code, that describe what the source code does. Looking at the following
code, can you understand what it does?
C = SQRT(A * A + B * B)
Deciphering this code is straightforward. This command multiplies two variables
by themselves, A and B, adds the results together, and finds the square
root of the sum, which gets stored in the C variable. However, knowing how
the command works doesn’t tell you what or why this code is doing this. By
adding comments to the source code, you can explain this, as follows:
‘ Calculates the hypotenuse of a triangle (C)
‘ using the Pythagoras theorem: C 2 = A 2 + B 2
C = SQRT(A * A + B * B)