Comparison Operators (Visual Basic)
The following are the comparison operators defined in Visual Basic.
< operator
<= operator
> operator
>= operator
= operator
<> operator
These operators compare two expressions to determine whether or not they are equal, and if not, how they differ. Is, IsNot, and Like are discussed in detail on separate Help pages. The relational comparison operators are discussed in detail on this page.
Syntax
result = expression1 comparisonoperator expression2
result = object1 [Is | IsNot] object2
result = string Like pattern
Parts
result
Required. A Boolean value representing the result of the comparison.
expression1, expression2
Required. Any expression.
comparisonoperator
Required. Any relational comparison operator.
object1, object2
Required. Any reference object names.
string
Required. Any String expression.
pattern
Required. Any String expression or range of characters.
Remarks
The following table contains a list of the relational comparison operators and the conditions that determine whether result is True or False.
| Operator | True if |
False if |
|---|---|---|
< (Less than) |
expression1 < expression2 |
expression1 >= expression2 |
<= (Less than or equal to) |
expression1 <= expression2 |
expression1 > expression2 |
> (Greater than) |
expression1 > expression2 |
expression1 <= expression2 |
>= (Greater than or equal to) |
expression1 >= expression2 |
expression1 < expression2 |
= (Equal to) |
expression1 = expression2 |
expression1 <> expression2 |
<> (Not equal to) |
expression1 <> expression2 |
expression1 = expression2 |
Note
The = Operator is also used as an assignment operator.
The Is operator, the IsNot operator, and the Like operator have specific comparison functionalities that differ from the operators in the preceding table.
Comparing Numbers
When you compare an expression of type Single to one of type Double, the Single expression is converted to Double. This behavior is opposite to the behavior found in Visual Basic 6.
Similarly, when you compare an expression of type Decimal to an expression of type Single or Double, the Decimal expression is converted to Single or Double. For Decimal expressions, any fractional value less than 1E-28 might be lost. Such fractional value loss may cause two values to compare as equal when they are not. For this reason, you should take care when using equality (=) to compare two floating-point variables. It is safer to test whether the absolute value of the difference between the two numbers is less than a small acceptable tolerance.
Floating-point Imprecision
When you work with floating-point numbers, keep in mind that they do not always have a precise representation in memory. This could lead to unexpected results from certain operations, such as value comparison and the Mod Operator. For more information, see Troubleshooting Data Types.
Comparing Strings
When you compare strings, the string expressions are evaluated based on their alphabetical sort order, which depends on the Option Compare setting.
Option Compare Binary bases string comparisons on a sort order derived from the internal binary representations of the characters. The sort order is determined by the code page. The following example shows a typical binary sort order.
A < B < E < Z < a < b < e < z < À < Ê < Ø < à < ê < ø
Option Compare Text bases string comparisons on a case-insensitive, textual sort order determined by your application's locale. When you set Option Compare Text and sort the characters in the preceding example, the following text sort order applies:
(A=a) < (À= à) < (B=b) < (E=e) < (Ê= ê) < (Ø = ø) < (Z=z)
Locale Dependence
When you set Option Compare Text, the result of a string comparison can depend on the locale in which the application is running. Two characters might compare as equal in one locale but not in another. If you are using a string comparison to make important decisions, such as whether to accept an attempt to log on, you should be alert to locale sensitivity. Consider either setting Option Compare Binary or calling the StrComp, which takes the locale into account.
Typeless Programming with Relational Comparison Operators
The use of relational comparison operators with Object expressions is not allowed under Option Strict On. When Option Strict is Off, and either expression1 or expression2 is an Object expression, the run-time types determine how they are compared. The following table shows how the expressions are compared and the result from the comparison, depending on the runtime type of the operands.
| If operands are | Comparison is |
|---|---|
Both String |
Sort comparison based on string sorting characteristics. |
| Both numeric | Objects converted to Double, numeric comparison. |
One numeric and one String |
The String is converted to a Double and numeric comparison is performed. If the String cannot be converted to Double, an InvalidCastException is thrown. |
Either or both are reference types other than String |
An InvalidCastException is thrown. |
Numeric comparisons treat Nothing as 0. String comparisons treat Nothing as "" (an empty string).
Overloading
The relational comparison operators (<. <=, >, >=, =, <>) can be overloaded, which means that a class or structure can redefine their behavior when an operand has the type of that class or structure. If your code uses any of these operators on such a class or structure, be sure you understand the redefined behavior. For more information, see Operator Procedures.
Notice that the = Operator can be overloaded only as a relational comparison operator, not as an assignment operator.
Example
The following example shows various uses of relational comparison operators, which you use to compare expressions. Relational comparison operators return a Boolean result that represents whether or not the stated expression evaluates to True. When you apply the > and < operators to strings, the comparison is made using the normal alphabetical sorting order of the strings. This order can be dependent on your locale setting. Whether the sort is case-sensitive or not depends on the Option Compare setting.
Dim x As testClass
Dim y As New testClass()
x = y
If x Is y Then
' Insert code to run if x and y point to the same instance.
End If
In the preceding example, the first comparison returns False and the remaining comparisons return True.
