Programming instructions

Understanding conditional processing 25

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:

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:

HTML and CFML tags executed if expression is True.

HTML and CFML tags executed if expression is False.

</cfif>