Getting Started Building ColdFusion MX Applications
CFML Basics

Understanding conditional processing

To this point, all the coding examples shown are considered linear coding examples. Linear code is when ColdFusion executes code starting with the first line on the page, and processes every line in order. Although you will use linear code in your applications, you will often write code that performs various actions based on conditions, such as the following:

• Determine if a user entered a value in a form field.
• Display results based on user input.
• Display messages based on the time of day.

You use conditional processing to customize the behavior of your application. Conditional processing facilitates decision making and lets you control how the code on a page is processed.

In ColdFusion, you implement conditional processing with flow control tags. These tags are similar to other programming language control elements, such as if, then, and else.

Conditional processing tags

ColdFusion provides several tags that let you control how a page is processed. When using these tags, you can facilitate decision making in your code. The most fundamental tags used to control code execution are the cfif, cfelse, and cfelseif tags. Because you will see and use these tags in Part II of this book, the following sections provide a basic introduction on how to use these tags. For more information about other conditional processing tags, including tags for looping, see Developing ColdFusion MX Applications with CFML.

Using cfif to evaluate true or false conditions

To create statements that let you evaluate conditions and perform an action based on the result, you use the cfif tag to create a cfif statement. The basic syntax for a cfif statement is as follows:

<cfif expression>

HTML and CFML tags executed if expression is True.

</cfif>

In the previous example, ColdFusion only executes the code inside the cfif statement if the expression evaluates to true. To perform actions if the expression is false, you can use the cfelse tag. For example, if the following cfif expression evaluates to false, then the code between the cfelse tag and the cfif tag is processed:

<cfif expression>

  HTML and CFML tags executed if expression is True.
<cfelse>
  HTML and CFML tags executed if expression is False.

</cfif>

Using cfelseif to evaluate multiple expressions

To evaluate multiple expressions in a cfif statement, you can use cfelseif and cfelse in your statement, for example:

<cfif expression 1>

  HTML and CFML tags executed if expression 1 is True.
<cfelseif expression 2>
  HTML and CFML tags executed if expression 2 is True.
<cfelse>
  HTML and CFML tags executed for expression(s) that is False.

</cfif>

The following example shows you how you can evaluate multiple expressions using these tags. In this example, you created a form in which users can enter their state to determine their state tax:

<cfoutput>

<cfif form.state IS "MA">
  #form.state# State Tax: 8.5%
<cfelseif form.state IS "VA">
  #form.state# State Tax: 8.2%
<cfelse>
  #form.state# State Tax Unknown
</cfif>

</cfoutput>

The output of this cfif statement is based on the value entered by the user. If the user enters MA in the state form field, the state tax results returned is 8.5%. If the user enters VA in the state form field, the state tax results returned is 8.2%. If the user enters any other state in the state form field, State Tax Unknown is returned.

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