ASP Primer: Functional VBScript
You've gotten a handle on the conditionals. You can do a loop. Now it's time to learn about some of the built in functions that make life a whole lot easier.
And now for my disclaimer. Many of the functions that we talk about below will have additional features that we will not cover in this short tutorial. If you would like more information on the functions or any of the other topics we cover in this series, be sure to check out Microsoft's online documentation at http://msdn.microsoft.com.
Do the Math
Even though you probably won't be doing much serious math in most of your ASP applications, it's still a good idea to review some of the more common math functions. Being that as it may, here are the more common VBScript mathematical functions:
Mathematics:


ABS( )  This stands for ABSolute value. An absolute value, if you
remember from math class, is simply taking any number and eliminating the
sign so that any number returned here is essentially a positive number. . 
INT( )  This function will probably get more use than any of the
other mathematical functions we list here with maybe the exception of the
randomizing functions below. What INT does is simply turn any decimal number
into an integer (whole) number. It does this by whacking off everything
after the decimal point. That means there is no rounding going on here, it
simply throws away the fractional part of any number that you give it. For
example, if you give INT( ) the number 7.694, it will return then
number 7.

LOG( )  This function returns the natural logarithm of the number
that you give it.

Trigonometry:


SIN( )  I'm sure you already guessed that this is sine. Now, I'm not
going to go into detail on the uses of sine because you probably already
know what sine is used for. If you don't, you may want to see if you can dig
up one of your old math books before you start plugging in this function.

COS( )  This function returns the cosine of the angle that you give
it.

TAN( )  This function returns the tangent of the angle that you give
it.

ATN( )  This function returns the arctangent of the number that you
give it.

Miscellaneous:


RANDOMIZE  This particular math function does not actually return a
result. What Randomize does is set a seed for random number generation. In
short, it gets the ball rolling so that you can generate random numbers.

RND( )  This is the function that actually generates a random number. Unlike our other math functions above, you don't actually give this function a number to crunch. To see how RANDOMIZE and RND( ) work handinhand, check out our practical example below. 
Before we get into the randomizing functions, let's take a second to look at how the other mathematical functions work. Using the mathematical functions above is quite simple. Here's an example of how to use TAN( ):
decTangent = TAN(intAngle)
It's as simple as giving the function a number to crunch and letting it do the rest. The above example applies to pretty much every function that we mentioned above with the exception of the randomizing functions.
RANDOMIZE and RND( ) are a bit different. In order to effectively demonstrate them in use I've come up with this installments practical example, a randomly displayed banner ad:
<% Option Explicit %>
<% ' Banner Ad
Rotation %>
<% Dim decRandomNumber %>
<% RANDOMIZE %>
<% decRandomNumber = RND( ) %>
<% If decRandomNumber > .5 then %>
<a HREF="http://www.adsite.com">
<IMG width="468" height="60" src="BannerAd1.jpg">
</a>
<% Else %>
<a HREF="http://www.otheradsite.com">
<IMG width="468" height="60" src="BannerAd2.jpg">
</a>
<% End If %>
Now for an explanation of how the code above works. First, we declare our variable that we are going to use to store our random number, decRandomNumber.
Next we use the RANDOMIZE function. This function sets the randomizing generator in motion by seeding it. (Random number generators work by using a complex algorithm that requires a seed number to kickstart the process. That seed number can be taken any number of ways but usually involves a combination of the current date and time.) You only need to use the RANDOMIZE function once on each ASP page since it simply gets the process started. It can be used more than once but it isn't necessary.
The next function that you will see is RND( ). RND( ) is the actual function that goes out and retrieves your random number. We set our decRandomNumber variable equal to the RND( ) function. This will set decRandomNumber equal to a random number between 0 and 1.
Once we have our random number set, it is a simple process of checking the number to see if it is greater than .5 or not. That is where the If .. Then statement comes in. If our number is greater than .5 then we display BannerAd1, otherwise we display BannerAd2.
Right now each ad will be displayed 50% of the time. To give more weight to one ad over another just change how you make the comparison. For example, if you change the first part of the If .. Then to say decRandomNumber > .75, BannerAd1 will only be displayed 25% of the time. You can also add additional banner ads by adding in an ElseIf or two. (Using the If .. Then, ElseIf and Else statements can be found here.)
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Messing with Strings
Let's move on to some string functions. You will probably find yourself using string functions infinitely more than the mathematical functions above. The reason is that most of the data you interact with on the web is in the form of strings, i.e. people's names, addresses, web URL's, email addresses, etc.
Here are some of the most commonly used string functions. I have tried to give an easy to understand example of each function. We'll discuss the practical applications of some of the functions later. Here they are:
Changing Strings:  
LCASE( )  This function does exactly what you might think. It takes
any string it gets and makes it all lower case. Example: Doing LCASE("Hello World!") will give you "hello world!" back.

UCASE( )  This function is, of course, the polar opposite of LCASE(
). UCASE( ) changes any given string to all upper case. Example: Taking the example above, doing UCASE("Hello World!") will give you back "HELLO WORLD!".

LTRIM( )  This function gets rid of extra spaces on the left side of
any string by just chopping them off. Example: If you give LTRIM( ) the string " There are 5 extra spaces to the left.", it will return a string like this "There are 5 extra spaces to the left."

RTRIM ( )  This function does the opposite of LTRIM( ). It
removes any extra spaces from the right side of any string. Example: The string "There are 5 spaces to the right of this string. " will be returned as "There are 5 spaces to the right of this string.".

TRIM( )  TRIM( ) then is a combination of the two above. It
will chop off any extra spaces before and after a given string. Example: The string " There are 5 spaces before and after this string. " will return a result of "There are 5 spaces before and after this string.".

REPLACE( )  Learn this one well. REPLACE( ) allows you to replace
any given set of characters in a string with another set of characters. Example: This function is a bit more complicated than the rest of the string functions above. It requires more information before it can do its thing. So, with that said, here is a some code to illustrate exactly how the function works: strMySentence = "I like ice cream!" strNewSentence = REPLACE(strMySentence,"like","love") The result of the code above would be that strNewSentence would now equal to "I love ice cream!". REPLACE( ) first wants to know what string it is to perform the replace on, then what word or set of characters it is looking for, and lastly what word or set of characters it is swapping in when it finds a match. If there is more than one match within a string it will replace all of the matches it finds.

All About the String:  
LEN( )  This is one of the few string functions that doesn't
actually return a string. Instead it returns the length of any given string
as an integer. In other words, it counts the number of characters, including
spaces, and gives you the total. Example: If you do LEN("Test String") you will get the number 11 as the result.

LEFT( )  This function allows you to get a selected section of a
string. It is done by giving the function the string you want a piece of and
the length of that piece. It then counts from the left to a specified length
and returns that piece of the string. Example: LEFT("I love ASP!",6) would return the string "I love", which is 6 characters from the left including the space.

RIGHT( )  This function does the exact same process as LEFT( )
except from the right. Example: RIGHT("I love ASP!",4) would return the string "ASP!", which is 4 characters from the right.

MID( )  As you might expect, MID( ) allows you to take a
string out of the middle of another string. For this particular function you
will need a starting point and the number of characters that you
want. Example: MID("I love ASP!",3,4) will give you "love" as the result. It starts at the third character "l" and snags it plus the next 3 characters for a total of 4.

INSTR( )  This function allows you to search for a string within a
string. It works much like REPLACE( ) does in that you give it a
string to search and a string to search for. The result it returns is the
character number of the beginning of the match, if it finds one. If it
doesn't find a match it will return a 0. Example: INSTR("I love ASP!","love") will return the integer 3. If you try INSTR("I love ASP!","like") it will return the integer 0. Here's an extra little tip about INSTR( ), INSTR("I love ASP!","asp",1) will ignore casesensitivity. In other words, the number one at the end of the function tells it to find a match ignoring case. The default is to find an exact match. The result of the example above would be 8. The result of this example, INSTR("I love ASP!","asp") would be 0, no match found. 
Now that you know some of the string functions that you have available to you, I thought it might be a good idea to give you some common uses for them.
UCASE( ) and LCASE( ): These are very useful in eliminating casesensitivity when you are making comparisons. For example, let's say someone enters an email address on a form to look up their account information. You don't want to tell them you can't find their account if they accidentally capitalized a character in their email. So, to eliminate that possibility you might want to take the email address they input on the form and transform it to all lower case with the LCASE( ) function before you make a comparison to the accounts in your database.
TRIM( ), LTRIM( ) and RTRIM( ): These functions are excellent for "cleaning up" a user's input. As a rule, I always use TRIM( ) on all input I get from users. I like to eliminate any extra spaces up front so that they don't cause me any problems later. I very rarely use LTRIM( ) and RTRIM( ).
REPLACE( ): This is one of the handiest functions around. You will find it very necessary for eliminating problems when interacting with a database using SQL. You will also find it very useful when trying to translate carriage returns into breaks (<BR>) in HTML. I will show you specific examples of how REPLACE( ) is a necessity when we get to some of the database stuff later.
LEN( ): This function I find most useful when determining whether a user's input is too long or too short. If you are storing user input into a database you will often have size limitations to contend with. This function can check those limits before you generate an error writing to your database. It is also very useful for parsing out search strings (we'll get to that later).
LEFT( ), RIGHT( ) and MID( ): These functions are great for chopping up user input into single words or phrases. They are most handy in cooperation with LEN( ) when separating out words in a user's search string. I sometimes use LEFT( ) to cut off user input that is too long.
INSTR( ): I find this function most useful in searching for illegal words. For example, let's say your ASP page is posting user messages to a bulletin board. The bulletin board is family oriented and you want to ensure that there is no bad language in any of the postings. You can use INSTR( ) to deny messages where you find offensive language.
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Nailing Down a Date & Time
As if you haven't had your fill of functions yet, here are some common functions used for manipulating date and time:
DATE( )  This function gets the current date.

TIME( )  This function gets the current time.

NOW( )  This function gets the current date and time.

MONTH( )  This function pulls the month out of any date/time string
variable and returns it as a integer.

DAY( )  This function pulls the day out of any date/time string
variable and returns it as a integer.

YEAR( )  This function pulls the year out of any date/time string
variable and returns it as a integer.

HOUR( )  This function pulls the hours out of any date/time string
variable and returns it as a integer.

MINUTE( )  This function pulls the minutes out of any date/time string
variable and returns it as a integer.

SECOND( )  This function pulls the seconds out of any date/time string
variable and returns it as a integer.

WEEKDAY( )  This function is one of the more handy ones. It takes any
date given it and tells you what day of the week it is. It does this by
returning an integer number that indicates the day of the week. If a 1 is
returned it is a Sunday, a 2 indicates a Monday, etc.

DATEDIFF( )  This function allows you get the difference between two
days. You can even select how the difference is calculated, i.e. days,
hours, minutes, etc. Here's how it works: dateDay1 = "1/1/2002" DATEDIFF("d",DATE( ),dateDay1) The example above compares today's date with the first day of 2002 and gives us the number of days between them. The "d" lets the function know to calculate the difference in days. We could have also used "h" for hours, "m" for months, "s" for seconds, etc. to calculate the difference.

DATEADD( )  As you would imagine, this function adds two dates together
and gives you the result. This function needs some very specific information
in order to complete its task. It must know the date it needs to add to, the
type of time that is being added (i.e. days, hours, minutes, etc.), and it
needs to know how much time to add. Here is an example: DATEADD("h",12,NOW( )) The function above will add 12 hours ("h") to today's date and time. The result will be a new date and time 12 hours from now. 
You probably won't find yourself manipulating dates and times as much as strings but you will use these functions quite a bit. Here are some practical uses for the functions above:
DATE( ), TIME( ) and NOW( ): You will be surprised how often you need to get the current date and time. I have used these functions for everything from displaying the current day to time stamping data that I send to a database. You will probably find DATE( ) and NOW( ) the most useful.
MONTH( ), DAY( ), HOUR( ), MINUTE( ), YEAR( ), SECOND( ): To be completely honest with you, I will rarely use any of these functions. It is useful, on occasion, to get the month, day or sometimes year out of a date but I rarely have used the HOUR( ), MINUTE( ) and SECOND( ) functions.
WEEKDAY( ): This is a very handy function for displaying a more full and formal date. I actually use this one quite a bit whenever I need to display a complete date.
DATEDIFF( ) and DATEADD( ): These functions are both very commonly used. I use DATEDIFF( ) mostly for determining whether or not to display some data that has an expiration attached to it. For example, displaying a special message about a current sale until the sale expires. I use the DATEADD( ) function for determining expiration dates. It is quite handy quickly calculating expiration dates for cookies and the like.
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What's Next?
That's it! This concludes your crash course in VBScript. Now, there is much more to VBScript than we have talked about up to this point but you have the basics. We will cover additional features of VBScript as we come across them later in this series.
Next it's on to some real ASP. You'll finally begin putting together the pieces and start creating some fullblown ASP applications.
In the next part of this series we will:

Talk to the user with Response.Write

Give directions to the user with Response.Redirect

Store info about the user with Response.Cookies