Operators

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You can use operators in formulas to perform arithmetic operations (+, -, *, / and ^) or logical comparisons (<, >, =, <=, >= and <>). You also can control the order of evaluation in a formula by enclosing expressions in parentheses. The ampersand (&) operator is used for the concatenation of character strings.

The abstraction for an operator is defined by the INOperator interface. The NFormulaEngine recognizes a predefined set of operators, which are enumerated by the OperatorType enumeration. By default when an instance of the NFormulaEngine is created it uses the default set of operators, which can be obtained from the DefaultOperators static field.

You can override the default operators by setting the CustomOperators property to an instance of the NOperatorContainer class, which contains your custom operators. A reference to the currently used set of operators can be obtained from the UsedOperators property. If custom operators are not used it returns the DefaultOperators.

When the operator arguments are of different type an automatic type conversion is attempted, whenever some of the arguments type do not match the action, which the operator performs. For example, the multiplication operator requires numeric arguments, and the ampersand (string concatenation) operator requires string arguments.

Following is detailed information about the different types of operators.

Arithmetic Operators

Arithmetic operators perform operations on numeric variants. The arithmetic operators arguments are automatically converted to compatible types (for example if you attempt to multiply a float variant with a double variant, the resulting variant will be of type double). The following table summarizes the current set of arithmetic operators:

Syntax	Name	Description	Example	Result
+	Unary plus	Does nothing - it is defined for completeness with the unary minus.	+10	10
-	Unary minus	Used to establish a number with a negative sign.	-10	-10
^	Exponentiation	Raises arg1 to the power of arg2.	10 ^ 2	100
*	Multiplication	Multiplies arg1 by arg2.	10 * 2	20
/	Division	Divides arg1 by arg2.	10 / 2	5
+	Addition	Adds arg2 to arg1.	10 + 2	12
-	Subtraction	Subtracts arg2 from arg1.	10 - 2	8

Comparison Operators

Comparison operators are used to construct logical expressions. A logical expression evaluates to a boolean variant with value true or false. The following table summarizes the current set of comparison operators:

Syntax	Name	Description	Example	Result
>	Greater than	Returns true if arg1 is greater than arg2. Otherwise returns false.	10 > 2	true
<	Less than	Returns true if arg1 is less than arg2. Otherwise returns false.	10 < 2	false
>=	Greater than or equal to	Returns true if arg1 is greater than or equal to arg2. Otherwise returns false.	10 >= 2	true
<=	Less than or equal to	Returns true if arg1 is less than or equal to arg2. Otherwise returns false.	10 <= 2	false
=	Equal to	Returns true if arg1 is equal to arg2. Otherwise returns false.	10 = 2	false
<>	Not equal to	Returns true if arg1 is not equal to arg2. Otherwise returns false.	10 <> 2	true

Ampersand Operator

The ampersand operator (&) is used to concatenate its arguments. You can use this operator to create new words and phrases. For example:

"hello" & " " & "world"

evaluates to:

"hello world"

Operators Priority

It is important to know that there is a priority assigned to each operator. If an expression contains sevaral operators, which are not enclosed in parentheses, the operator with the highest priority is evaluated first. For example:

10 + 20 * 2

evaluates to 50, because the multiplication operator will be evaluated first (it has a higher priority than the addition operator).

(10 + 20) * 2

evaluates to 60, since the parentheses override the default way in which the expression is evaluated.

The following table summarizes the operators priority:

Priority	Operators
1	Unary plus (+) Unary minus (-)
2	Exponentiation (^)
3	Multiplication (*) Division (/)
4	Addition (+) Subtraction (-)
5	String concatenation (&)
6	Greater than (>) Greater than or equal to (>=) Less than (<) Less than or equal to (<=)
7	Equal (=) Not equal (<>)