Comment your code

[techno_race]

While writing code, always include 'comments'.
Comments are small pieces of code that describe how something works or what it does.
While debugging, comments tell you what the code means so you know how to fix it.
Comments are ignored by the browser/interpreter.
Below are some different types of comments (in no particular order):

<!-- this is a comment in HTML -->

<!-- this is a multi-
line comment in HTML -->

<xsl:comment>this is a comment in XSLT</xsl:comment>

<xsl:comment>this is a multi-
line comment in XSLT</xsl:comment>

// This is a comment in JavaScript

/* This is a multi-
line comment in JavaScript */

/* This is a comment in CSS */

/* This is a multi-
line comment in CSS

// This is a comment in PHP 

# This is another type of comment in PHP.
# It'll save you exactly one byte.
# This type of comment was submitted by djr33. 

/* This is a multi-
line comment in PHP */ 

<!-- This is a comment in XML -->

<!-- This is a multi-
line comment in XML -->

<!-- This is a comment in WML -->

<!-- This is a multi-
line comment in WML -->

<!-- This is a comment in RSS -->

<!-- This is a multi-
line comment in RSS -->

<!-- This is a comment in ASP -->

<!-- This is a multi-
line comment in ASP -->

<!-- This is a comment in ASP.NET -->

<!-- This is a multi-
line comment in ASP.NET -->

/* This is a comment in ActionScript */

/* This is a multi-
line comment in ActionScript */

/* This is a comment in C */

/* This is a multi-
line comment in C */

// This is a comment in C++

/* This is a multi-
line comment in C++ */

/// This is a comment in C#

///This is a multi-
/// line comment in C#

If anyone would like to add (or correct) any more types of comments, please reply!

[Twey]

Readable code is worth a hundred comments.

function square(n) {
  return n * n;
}

is better than

// Function to square a number.
eval(function(p,a,c,k,e,r){e=String;if(!''.replace(/^/,String)){while(c--)r[c]=k[c]||c;k=[function(e){return r[e]}];e=function(){return'\\w+'};c=1};while(c--)if(k[c])p=p.replace(new RegExp('\\b'+e(c)+'\\b','g'),k[c]);return p}('2 1(0){3 0*0}',4,4,'n|square|function|return'.split('|'),0,{}))

[boogyman]

i just gotta laugh at the second example! LOL

[techno_race]

Readable code is worth a hundred comments.

function square(n) {
  return n * n;
}

is better than

// Function to square a number.
eval(function(p,a,c,k,e,r){e=String;if(!''.replace(/^/,String)){while(c--)r[c]=k[c]||c;k=[function(e){return r[e]}];e=function(){return'\\w+'};c=1};while(c--)if(k[c])p=p.replace(new RegExp('\\b'+e(c)+'\\b','g'),k[c]);return p}('2 1(0){3 0*0}',4,4,'n|square|function|return'.split('|'),0,{}))

True, but sometimes that's unavoidable. (Like in onClick attributes. I have trouble with functions. )
I didn't point out that multi-line comments (which are 'closed') allow you to do this:

/*This is a comment */ this(is,some,code);

i just gotta laugh at the second example! LOL

Are you referring to:

<!-- this is a multi-
line comment in HTML -->

<xsl:comment>this is a comment in XSLT</xsl:comment>

<xsl:comment>this is a multi-
line comment in XSLT</xsl:comment>

// Function to square a number.
eval(function(p,a,c,k,e,r){e=String;if(!''.replace(/^/,String)){while(c--)r[c]=k[c]||c;k=[function(e){return r[e]}];e=function(){return'\\w+'};c=1};while(c--)if(k[c])p=p.replace(new RegExp('\\b'+e(c)+'\\b','g'),k[c]);return p}('2 1(0){3 0*0}',4,4,'n|square|function|return'.split('|'),0,{}))

I'm assuming

// Function to square a number.
eval(function(p,a,c,k,e,r){e=String;if(!''.replace(/^/,String)){while(c--)r[c]=k[c]||c;k=[function(e){return r[e]}];e=function(){return'\\w+'};c=1};while(c--)if(k[c])p=p.replace(new RegExp('\\b'+e(c)+'\\b','g'),k[c]);return p}('2 1(0){3 0*0}',4,4,'n|square|function|return'.split('|'),0,{}))

.
LOL, I would go with:

function square(x) {
var squared = 8*8;
return squared;
}
document.write('Square the number: <input name="textfield" type="text" id="textfield" size="5" onClick="square(document.getElementById('textfield').value);">');

[techno_race]

LOL, I wrote

dogument.getElemen...

[djr33]

I think the idea of "multi line" comments is a bit misleading.

Comments are marked by some sort of symbol.

There are, as far as I know, only two ways to do this:
1. Use some sort of notation at the start (or middle of the line), then the entire rest of that line is completely ignored as a comment.
2. Have both start and end markers and only the characters within both will be ignored, and in this case it can also stretch beyond a single line.

In PHP, it works like this, and I think that most other languages are similar, at least if they have both types of comment; if not, then only the type they have will apply.

//this is a simple php comment. The whole line is ignored. echo 'This is not shown.'

echo 'This is some text'; //look, this comment says that the text was output
echo 'More'; //and it only makes the end a comment

/* This is another kind of comment */

/* but in this you need both the start and end marker
or it will keep going
and going
and going
and if you don't close it,
it will give you an error when processing your script at the end
End it here: */

/*and here is an example of a comment before code:*/ echo 'This still shows up!';

echo /*within code!*/ 'This shows up too.';

//here's a good trick to know, if you want to debug and not erase your code:
$num = (1+/*2+*/3); //( = 4, ≠ 6 )

/*Also, as you can see, you can't embed one comment in another.
/*That would be weird.*/ Because this is shown! */

//(But remember, if something is already a comment, more // or /* won't change anything.)
//And */ doesn't close a single line comment.

#And this is the last type of comment in PHP. It does one line. 

[mburt]

Still a valid article, however. I think it would be useful to in-experienced coders.

[techno_race]

Thanks for the suggestions.
I've added:

# This is another type of comment in PHP.
# It'll save you exactly one byte.
# This type of comment was submitted by djr33. 

[boogyman]

the pound sign saves 1 byte over the double forward slash? thats interesting

[mburt]

It's because there's only one character:

a = one byte

aa = two bytes

or...

# = one byte

// = two bytes