Getting Started Building ColdFusion MX Applications
CFML Basics

Working with CFML expressions

Expressions are an important part of the ColdFusion language. Expressions are a collection of different elements, ColdFusion variables, functions, and operators. You can think of them as strings of text that consist of one or more of the following elements:

• Literal text (string), numbers, dates, and other values
• Variables
• Functions
• Operators (& for joining statements, + for addition, and so on)

Many examples of expressions were shown in this chapter; for example:

• #variables.my_full_name#
• DateFormat(Now())
• my_first_name= "Kaleigh"

When you build expressions in ColdFusion, you can include simple and complex elements; how you represent these elements determines how ColdFusion processes your program.

Building expressions

In ColdFusion, you build expressions as you need them. The expressions can include simple elements, such as the expressions shown previously, or they can include complex elements, such as arithmetic functions, strings, and decision operators. (You build some complex expressions in Part II of this book.)

As mentioned, it is important that elements are identified properly in your expression so ColdFusion processes them as expected, and you can avoid unnecessary errors. When writing expressions, consider the following coding practices:

• Character case consistency
• When to use the pound (#) sign
• When quotation marks are needed

Specifying a consistent character case

Because the ColdFusion server is case-insensitive, you can write expressions using all uppercase, all lowercase, or mixed case. However, for code readability and consistency, you should use the same character case in all your programs. If you write your programs using the same case rules, you might prevent errors from occurring when you combine CFML on a page with case-sensitive languages, such as JavaScript.

Specifying pound signs to denote functions or variables

In ColdFusion, you specify pounds signs to denote functions and variables within a string of text. You use pounds signs to show the results of the function or variable on the page. Pounds signs instruct the ColdFusion server to evaluate the function (or variable) between the pound signs and display the value. The value of the function (or variable) appears in the browser as a result.

The following list identifies some common ways to use pound signs:

• In the following example, you include the pound signs to return the value to a page:

  <cfoutput> Hello #variables.my_first_name# </cfoutput>
  

  If you omit the pound signs, the text, not the value, appears on the page.

• In the following example, you do not include the pound signs because you are using cfset to assign one variable's value to another value:

  <cfset my_full_name = variables.my_first_name & " " & variables.my_last_name>
  

• To display a pound sign on a page, you must designate the pound sign as a literal character. You do this by using two pound signs (##); for example:

  <cfoutput>
  ##1: Your name.
  </cfoutput>
  

  The result is the following output:

  #1. Your name.

For more information and examples on using pound signs in expressions, see Developing ColdFusion MX Applications with CFML.

Specifying quotation marks around values

When assigning literal values to variables, you must surround the literal value with double quotation marks or single quotation marks. ColdFusion interprets the content between the quotation marks as a literal value and assigns that value to the variable; for example:

<cfset my_first_name = "Kaleigh">

<cfset my_last_name = "Smith">

<cfset my_age = 5>

ColdFusion instantiates the variable my_first_name to the string literal Kaleigh. Further, Smith is assigned to the variable my_last_name and 5 is assigned to age.

When referencing a variable by its name, you do not surround the name with quotation marks; for example:

<cfset the_string = "My name is " & variables.my_first_name & 
" and my age is " & variables.my_age>

My name is is literal text and, you therefore, surround it with quotation marks. The variable references variables.my_first_name and variables.my_age are not surrounded by quotation marks. ColdFusion uses the values of the referenced variables (Kaleigh and 5, respectively) when assigning the value to the variable the_string.

To display quotation marks on a page as literal characters, you must double the quotation marks; for example:

<cfset mystring = "We all shouted ""Happy Birthday"" when he entered the room.">

<cfoutput>
#mystring#
</cfoutput>

The result is the following output:

We all shouted "Happy Birthday" when he entered the room.

Specifying operators in expressions

In ColdFusion, you use operators to test conditions; for example, you use the IS operator to test for equality. When using operators in expressions, you must only use supported logical operators that ColdFusion can interpret properly. For example, if you use the greater than operator (>)or the less than operator (<), ColdFusion interprets these operators as the start or end of a tag.

The following table lists the nonsupported logical operators and their equivalent ColdFusion operators:

Nonsupported logical operator	Equivalent ColdFusion decision operator	Description
=	IS, EQUAL, EQ	Tests for equality.
<	LT, LESS THAN	Tests for less than.
<=	LTE, LE, LESS THAN OR EQUAL TO	Tests for less than or equal to.
>	GT GREATER THAN	Tests for greater than.
>=	GTE, GREATER THAN OR EQUAL TO	Tests for greater than or equal to
< >	IS NOT, NEQ, NOT EQUAL	Tests for nonequality.
	CONTAINS	Tests whether a value is contained within a second value.
	DOES NOT CONTAIN	Tests whether a value is not contained within a second value.

Arithmetic operators

The following table lists the arithmetic operators that ColdFusion supports:

Operators	Description
+, -, *, /	The basic arithmetic operators: addition, subtraction, multiplication, and division. In the case of division, the right operand cannot be zero.
+, -	Unary arithmetic operators for setting the sign of a number either positive or negative (+ or -).
Mod	Returns the remainder (modulus) after a number is divided by a divisor. The result has the same sign as the divisor. The right operand cannot be zero; for example: 11 MOD 4 is 3.
\	Divides two integer values. Use the \ (trailing slash) to separate the integers. The right operand cannot be zero; for example: 9 \ 4 is 2.
^	Returns the result of a number raised to a power (exponent). Use the ^ (caret) to separate the number from the power. The left operand cannot be zero; for example: 2 ^ 3 is 8.

String operator

The following table describes the one ColdFusion string operator that is a concatenation operator:

Operator	Description
&	Concatenates strings.

Copyright © 2002, Macromedia Inc. All rights reserved.

Comments