Login | Register | FAQ
Anonymous

Lesson 6: Conditions

Conditions are used to execute part of a script only if some predefined requirements (conditions) are fulfilled. For example, a condition could be that a date must be after 1/1 2012 or that a variable is greater than 7.

If... Then ... Else

The first type of condition we will look at is the DocumentationIf-Then-Else condition, which has the following syntax:


	If condition Then
	   statment
	Else
	   statement
	End If
	
	

Again, the syntax is very close to ordinary English: If a condition is met Then execute something or Else execute something else.

In lesson 4, you learned how to find the number of a month. In the following example, we will use the month number in DocumentationIf-Then-Else condition to find out what season it is:


	<html>
	<head>
	<title>Loops</title>
	</head>
	<body>
	<%

	If Month (Date) = 3 Then

	   Response.Write "<p>Now it's spring!</p>"
	Else
	   Response.Write "<p>I do not know what season it is!</p>"	


	End If

	%>
	</body>
	</html>
	
	

As you can see, it's not a particularly smart condition - it only works when it's March!

However, there are plenty of ways to improve the condition and make it more precise. Below are listed comparison operators that can be used in the statement:

= Equals
< Less than
> Greater than
<= Less than or equal to
> = Greater than or equal to
<> Not equal to

In addition, there are some logical operators:

AND
OR
NOT

The operators can be used to develop more precise conditions, so now we can expand the above example to include all the spring months:


	<html>
	<head>
	<title>Loops</title>

	</head>
	<body>
	<%

	If Month(Date)> = 3 AND Month(Date) <= 5 Then

	   Response.Write "<p>Now it's spring!</p>"

	Else
	   Response.Write "<p>Now it's either winter, summer or autumn!</p>"

	End If

	%>
	</body>
	</html>

	
	

Let us take a closer look at the extended condition:

	Month(Date)> = 3 AND Month(Date) <= 5 

	
	

The condition can be translated into:

If the month is greater than or equal to 3, and the month is less than or equal to 5

Smart, eh? Operators play a significant role in many different parts of ASP.

But it still only works with March, April and May. All other months are not yet covered by the condition. Let us try to develop the condition a little more.

If ... Then ... ElseIf ... Else

Using ElseIf, we can expand the condition and make it work for all months:


	<html>
	<head>
	<title>Loops</title>

	</head>
	<body>
	<%

	If Month(Date)> = 3 AND Month(Date) <= 5 Then

	   Response.Write "<p>Now it's spring!</p>"

	Elseif Month(Date)> = 6 AND Month(Date) <= 8 Then
	   Response.Write "<p>Now it's summer!</p>"

	Elseif Month(Date)> = 9 AND Month(Date) <= 11 Then
	   Response.Write "<p>Now it's autumn!</p>"

	Else

	   Response.Write "<p>Now is the winter!</p>"
	End If

	%>
	</body>
	</html>

	
	

To write conditions is all about thinking logically and being methodical. The example above is pretty straightforward, but conditions can get very complex.

Select ... Case

Another way of writing conditions is to use the DocumentationSelect Case method:


	Select Case Expression

	Case 1 
	   statement

	Case 2 
	   statement

	Case Else
	   statement

	End Select
	
	

This method is based on an expression and then list different "answers" or "values" with related statements. The easiest way to explain the method is to show an example.

As you may remember from lesson 4, the function DocumentationWeekday returns the current weekday. This can be used in an example where we write the name of the day (instead of a number):


	<html>
	<head>
	<title>Loops </title>
	</head>
	<body>
	<%

	Select Case Weekday(Now,vbMonday)

	Case 1
	   Response.Write "Monday"
	Case 2
	   Response.Write "Tuesday"
	Case 3

	   Response.Write "Wednesday"

	Case 4
	   Response.Write "Thursday"
	Case 5
	   Response.Write "Friday"

	Case 6
	   Response.Write "Saturday"
	Case Else

	   Response.Write "Sunday"

	End Select

	%>
	</body>
	</html>
	
	

Often DocumentationSelect Case can be a good alternative to DocumentationIf-Then-Else. What you should use in a given situation depends on which method you find easiest and most logical. Making your scripts logical and clear can be a great challenge.

In the next lesson, we will look at how you can add comments to your scripts to explain how they work. Good comments can be crucial if you or somebody else has to make changes in your codes at a later stage.



<< Lesson 5: Loops

Lesson 7: Comment your scripts >>