关于Visual Basic script 的学习

				
				
				VBScript Operators 
				
				
				
				
				
				
				
				
				
				
				
				
				
				
				Microsoft® Visual Basic® Scripting Edition
				VBScript Operators
				
				
				
				 VBScript Tutorial  Previous | Next 
				
				
				
				 
				 
				
				
				
				
				VBScript has a full range of operators, including arithmetic operators, comparison operators, concatenation operators, and logical operators. 
				Operator Precedence
				When several operations occur in an expression, each part is evaluated and resolved in a predetermined order called operator precedence. You can use parentheses to override the order of precedence and force some parts of an expression to be evaluated before others. Operations within parentheses are always performed before those outside. Within parentheses, however, standard operator precedence is maintained. 
				
				When expressions contain operators from more than one category, arithmetic operators are evaluated first, comparison operators are evaluated next, and logical operators are evaluated last. Comparison operators all have equal precedence; that is, they are evaluated in the left-to-right order in which they appear. Arithmetic and logical operators are evaluated in the following order of precedence.
				
				
				
					Arithmetic
					Comparison
					Logical
				
				
					Description
					Symbol
				  	Description
					Symbol
					Description
					Symbol
				
				
					Exponentiation
					^
				  	Equality
					=
					Logical negation
					Not
				
				
					Unary negation
					-
				  	Inequality
					<>
					Logical conjunction
					And
				
				
					Multiplication
					*
					Less than
					<
					Logical disjunction
					Or
				
				
					Division
					/
					Greater than
					>
					Logical exclusion
					Xor
				
				
					Integer division
					\
					Less than or equal to
					<=
					Logical equivalence
					Eqv
				
				
					Modulus arithmetic
					Mod
					Greater than or equal to
					>=
					Logical implication
					Imp
				
				
					Addition
					+
					Object equivalence
					Is
					  
					  
				
				
					Subtraction
					-
					  
					  
					  
					  
				
				
					String concatenation
					&
					  
					  
					  
					  
				
				
				
				
				When multiplication and division occur together in an expression, each operation is evaluated as it occurs from left to right. Likewise, when addition and subtraction occur together in an expression, each operation is evaluated in order of appearance from left to right.
				
				The string concatenation (&) operator is not an arithmetic operator, but in precedence it does fall after all arithmetic operators and before all comparison operators. The Is operator is an object reference comparison operator. It does not compare objects or their values; it checks only to determine if two object references refer to the same object.
				
				
				
				© 1997 by Microsoft Corporation. All rights reserved.