VB.NET Operators and Expressions

An operator is a code element that performs an operation on one or more code elements that hold values. Value elements include variables, constants, literals, properties, returns from Function and Operator procedures, and expressions.

An expression is a series of value elements combined with operators, which yields a new value. The operators act on the value elements by performing calculations, comparisons, or other operations.

Types of Operators

Visual Basic provides the following types of operators:

Arithmetic Operators perform familiar calculations on numeric values, including shifting their bit patterns.
Comparison Operators compare two expressions and return a Boolean value representing the result of the comparison.
Concatenation Operators join multiple strings into a single string.
Logical and Bitwise Operators in Visual Basic combine Boolean or numeric values and return a result of the same data type as the values.

The value elements that are combined with an operator are called operands of that operator. Operators combined with value elements form expressions, except for the assignment operator, which forms a statement. For more information, see Statements.

Evaluation of Expressions

The end result of an expression represents a value, which is typically of a familiar data type such as Boolean, String, or a numeric type.

The following are examples of expressions.

5 + 4

' The preceding expression evaluates to 9.

15 * System.Math.Sqrt(9) + x

' The preceding expression evaluates to 45 plus the value of x.

"Concat" & "ena" & "tion"

' The preceding expression evaluates to "Concatenation".

763 < 23

' The preceding expression evaluates to False.

Several operators can perform actions in a single expression or statement, as the following example illustrates.

x = 45 + y * z ^ 2

In the preceding example, Visual Basic performs the operations in the expression on the right side of the assignment operator (=), then assigns the resulting value to the variable x on the left. There is no practical limit to the number of operators that can be combined into an expression, but an understanding of Operator Precedence in Visual Basic is necessary to ensure that you get the results you expect.

Common Tasks Performed with Visual Basic Operators

Operators perform many common tasks involving one or more expressions called operands.

Arithmetic and Bit-shift Tasks

The following table summarizes the available arithmetic and bit-shift operations.

To	See
Add one numeric value to another	+ Operator
Subtract one numeric value from another	- Operator (Visual Basic)
Reverse the sign of a numeric value	- Operator (Visual Basic)
Multiply one numeric value by another	* Operator
Divide one numeric value into another	/ Operator (Visual Basic)
Find the quotient of one numeric value divided by another (without the remainder)	\ Operator (Visual Basic)
Find the remainder of one numeric value divided by another (without the quotient)	Mod Operator
Raise one numeric value to the power of another	^ Operator
Shift the bit pattern of a numeric value to the left	<< Operator
Shift the bit pattern of a numeric value to the right	>> Operator

Comparison Tasks

The following table summarizes the available comparison operations.

To	See
Determine whether two values are equal	= Operator (Comparison Operators in Visual Basic)
Determine whether two values are unequal	<> Operator (Comparison Operators in Visual Basic)
Determine whether one value is less than another	< Operator (Comparison Operators in Visual Basic)
Determine whether one value is greater than another	> Operator (Comparison Operators in Visual Basic)
Determine whether one value is less than or equal to another	<= Operator (Comparison Operators in Visual Basic)
Determine whether one value is greater than or equal to another	>= Operator (Comparison Operators in Visual Basic)
Determine whether two object variables refer to the same object instance	Is Operator
Determine whether two object variables refer to different object instances	IsNot Operator
Determine whether an object is of a specific type	TypeOf Operator

Concatenation Tasks

The following table summarizes the available concatenation operations.

To	See
Join multiple strings into a single string	& Operator (Concatenation Operators in Visual Basic)
Join numeric values with string values	+ Operator (Concatenation Operators in Visual Basic)

Logical and Bitwise Tasks

The following table summarizes the available logical and bitwise operations.

To	See
Perform logical negation on a Boolean value	Not Operator
Perform logical conjunction on two Boolean values	And Operator
Perform inclusive logical disjunction on two Boolean values	Or Operator
Perform exclusive logical disjunction on two Boolean values	Xor Operator
Perform short-circuited logical conjunction on two Boolean values	AndAlso Operator
Perform short-circuited inclusive logical disjunction on two Boolean values	OrElse Operator
Perform bit-by-bit logical conjunction on two integral values	And Operator
Perform bit-by-bit inclusive logical disjunction on two integral values	Or Operator
Perform bit-by-bit exclusive logical disjunction on two integral values	Xor Operator
Perform bit-by-bit logical negation on an integral value	Not Operator

Arithmetic Operators in Visual Basic

Arithmetic operators are used to perform many of the familiar arithmetic operations that involve the calculation of numeric values represented by literals, variables, other expressions, function and property calls, and constants. Also classified with arithmetic operators are the bit-shift operators, which act at the level of the individual bits of the operands and shift their bit patterns to the left or right.

Arithmetic Operations

You can add two values in an expression together with the + Operator, or subtract one from another with the - Operator (Visual Basic), as the following example demonstrates.

Dim x As Integer
x = 67 + 34
x = 32 - 12

Negation also uses the - Operator (Visual Basic), but with only one operand, as the following example demonstrates.

Dim x As Integer = 65
Dim y As Integer
y = -x

Multiplication and division use the * Operator and / Operator (Visual Basic), respectively, as the following example demonstrates.

Dim y As Double
y = 45 * 55.23
y = 32 / 23

Exponentiation uses the ^ Operator, as the following example demonstrates.

Dim z As Double
z = 23 ^ 3
' The preceding statement sets z to 12167 (the cube of 23).

Integer division is carried out using the \ Operator (Visual Basic). Integer division returns the quotient, that is, the integer that represents the number of times the divisor can divide into the dividend without consideration of any remainder. Both the divisor and the dividend must be integral types (SByte, Byte, Short, UShort, Integer, UInteger, Long, and ULong) for this operator. All other types must be converted to an integral type first. The following example demonstrates integer division.

Dim k As Integer
k = 23 \ 5
' The preceding statement sets k to 4.

Modulus arithmetic is performed using the Mod Operator. This operator returns the remainder after dividing the divisor into the dividend an integral number of times. If both divisor and dividend are integral types, the returned value is integral. If divisor and dividend are floating-point types, the returned value is also floating-point. The following example demonstrates this behavior.

Dim x As Integer = 100
Dim y As Integer = 6
Dim z As Integer
z = x Mod y
' The preceding statement sets z to 4.

Dim a As Double = 100.3
Dim b As Double = 4.13
Dim c As Double
c = a Mod b
' The preceding statement sets c to 1.18.

Attempted Division by Zero

Division by zero has different results depending on the data types involved. In integral divisions (SByte, Byte, Short, UShort, Integer, UInteger, Long, ULong), the .NET Framework throws a DivideByZeroException exception. In division operations on the Decimal or Single data type, the .NET Framework also throws a DivideByZeroException exception.

In floating-point divisions involving the Double data type, no exception is thrown, and the result is the class member representing NaN, PositiveInfinity, or NegativeInfinity, depending on the dividend. The following table summarizes the various results of attempting to divide a Double value by zero.

Dividend data type	Divisor data type	Dividend value	Result
Double	Double	0	NaN (not a mathematically defined number)
Double	Double	> 0	PositiveInfinity
Double	Double	< 0	NegativeInfinity

When you catch a DivideByZeroException exception, you can use its members to help you handle it. For example, the Message property holds the message text for the exception. For more information, see Try...Catch...Finally Statement.

Bit-Shift Operations

A bit-shift operation performs an arithmetic shift on a bit pattern. The pattern is contained in the operand on the left, while the operand on the right specifies the number of positions to shift the pattern. You can shift the pattern to the right with the >> Operator or to the left with the << Operator.

The data type of the pattern operand must be SByte, Byte, Short, UShort, Integer, UInteger, Long, or ULong. The data type of the shift amount operand must be Integer or must widen to Integer.

Arithmetic shifts are not circular, which means the bits shifted off one end of the result are not reintroduced at the other end. The bit positions vacated by a shift are set as follows:

0 for an arithmetic left shift
0 for an arithmetic right shift of a positive number
0 for an arithmetic right shift of an unsigned data type (Byte, UShort, UInteger, ULong)
1 for an arithmetic right shift of a negative number (SByte, Short, Integer, or Long)

The following example shifts an Integer value both left and right.

Dim lResult, rResult As Integer
Dim pattern As Integer = 12
' The low-order bits of pattern are 0000 1100.
lResult = pattern << 3
' A left shift of 3 bits produces a value of 96.
rResult = pattern >> 2
' A right shift of 2 bits produces value of 3.

Arithmetic shifts never generate overflow exceptions.

Bitwise Operations

In addition to being logical operators, Not, Or, And, and Xor also perform bitwise arithmetic when used on numeric values. For more information, see "Bitwise Operations" in Logical and Bitwise Operators in Visual Basic.

Type Safety

Operands should normally be of the same type. For example, if you are doing addition with an Integer variable, you should add it to another Integer variable, and you should assign the result to a variable of type Integer as well.

One way to ensure good type-safe coding practice is to use the Option Strict Statement. If you set Option Strict On, Visual Basic automatically performs type-safe conversions. For example, if you try to add an Integer variable to a Double variable and assign the value to a Double variable, the operation proceeds normally, because an Integer value can be converted to Double without loss of data. Type-unsafe conversions, on the other hand, cause a compiler error with Option Strict On. For example, if you try to add an Integer variable to a Double variable and assign the value to an Integer variable, a compiler error results, because a Double variable cannot be implicitly converted to type Integer.

If you set Option Strict Off, however, Visual Basic allows implicit narrowing conversions to take place, although they can result in the unexpected loss of data or precision. For this reason, we recommend that you use Option Strict On when writing production code. For more information, see Widening and Narrowing Conversions.

Comparison Operators in Visual Basic

Comparison operators compare two expressions and return a Boolean value that represents the relationship of their values. There are operators for comparing numeric values, operators for comparing strings, and operators for comparing objects. All three types of operators are discussed herein.

Comparing Numeric Values

Visual Basic compares numeric values using six numeric comparison operators. Each operator takes as operands two expressions that evaluate to numeric values. The following table lists the operators and shows examples of each.

Operator	Condition tested	Examples
= (Equality)	Is the value of the first expression equal to the value of the second?	23 = 33 ' False 23 = 23 ' True 23 = 12 ' False
<> (Inequality)	Is the value of the first expression unequal to the value of the second?	23 <> 33 ' True 23 <> 23 ' False 23 <> 12 ' True
< (Less than)	Is the value of the first expression less than the value of the second?	23 < 33 ' True 23 < 23 ' False 23 < 12 ' False
> (Greater than)	Is the value of the first expression greater than the value of the second?	23 > 33 ' False 23 > 23 ' False 23 > 12 ' True
<= (Less than or equal to)	Is the value of the first expression less than or equal to the value of the second?	23 <= 33 ' True 23 <= 23 ' True 23 <= 12 ' False
>= (Greater than or equal to)	Is the value of the first expression greater than or equal to the value of the second?	23 >= 33 ' False 23 >= 23 ' True 23 >= 12 ' True

Comparing Strings

Visual Basic compares strings using the Like Operator as well as the numeric comparison operators. The Like operator allows you to specify a pattern. The string is then compared against the pattern, and if it matches, the result is True. Otherwise, the result is False. The numeric operators allow you to compare String values based on their sort order, as the following example shows.

"73" < "9"

' The result of the preceding comparison is True.

The result in the preceding example is True because the first character in the first string sorts before the first character in the second string. If the first characters were equal, the comparison would continue to the next character in both strings, and so on. You can also test equality of strings using the equality operator, as the following example shows.

"734" = "734"

' The result of the preceding comparison is True.

If one string is a prefix of another, such as "aa" and "aaa", the longer string is considered to be greater than the shorter string. The following example illustrates this.

"aaa" > "aa"

' The result of the preceding comparison is True.

The sort order is based on either a binary comparison or a textual comparison depending on the setting of Option Compare. For more information see Option Compare Statement.

Comparing Objects

Visual Basic compares two object reference variables with the Is Operator and the IsNot Operator. You can use either of these operators to determine if two reference variables refer to the same object instance. The following example illustrates this.

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, x Is y evaluates to True, because both variables refer to the same instance. Contrast this result with the following example.

Dim x As New customer()
Dim y As New customer()
If x Is y Then
    ' Insert code to run if x and y point to the same instance.
End If

In the preceding example, x Is y evaluates to False, because although the variables refer to objects of the same type, they refer to different instances of that type.

When you want to test for two objects not pointing to the same instance, the IsNot operator lets you avoid a grammatically clumsy combination of Not and Is. The following example illustrates this.

Dim a As New classA()
Dim b As New classB()
If a IsNot b Then
    ' Insert code to run if a and b point to different instances.
End If

In the preceding example, If a IsNot b is equivalent to If Not a Is b.

Comparing Object Type

You can test whether an object is of a particular type with the TypeOf...Is expression. The syntax is as follows:

TypeOf <objectexpression> Is <typename>

When typename specifies an interface type, then the TypeOf...Is expression returns True if the object implements the interface type. When typename is a class type, then the expression returns True if the object is an instance of the specified class or of a class that derives from the specified class. The following example illustrates this.

Dim x As System.Windows.Forms.Button
x = New System.Windows.Forms.Button()
If TypeOf x Is System.Windows.Forms.Control Then
    ' Insert code to run if x is of type System.Windows.Forms.Control.
End If

In the preceding example, the TypeOf x Is Control expression evaluates to True because the type of x is Button, which inherits from Control.

For more information, see TypeOf Operator.

How to: Test Whether Two Objects Are the Same

If you have two variables that refer to objects, you can use either the Is or IsNot operator, or both, to determine whether they refer to the same instance.

To test whether two objects are the same

Use the Is Operator or the IsNot Operator with the two variables as operands.
VB

Public Sub processControl(ByVal f As System.Windows.Forms.Form, 
    ByVal c As System.Windows.Forms.Control)
    Dim active As System.Windows.Forms.Control = f.ActiveControl
    If (active IsNot Nothing) And (c Is active) Then
        ' Insert code to process control c
    End If
    Return
End Sub

You might want to take a certain action depending on whether two objects refer to the same instance. The preceding example compares control c against the active control on form f. If there is no active control, or if there is one but it is not the same control instance as c, then the If statement fails and the procedure returns without further processing.

Whether you use Is or IsNot is a matter of personal convenience to you. One might be easier to read than the other in a given expression.

How to: Match a String against a Pattern

If you want to find out if an expression of the String Data Type satisfies a pattern, then you can use the Like Operator.

Like takes two operands. The left operand is a string expression, and the right operand is a string containing the pattern to be used for matching. Like returns a Boolean value indicating whether the string expression satisfies the pattern.

You can match each character in the string expression against a specific character, a wildcard character, a character list, or a character range. The positions of the specifications in the pattern string correspond to the positions of the characters to be matched in the string expression.

To match a character in the string expression against a specific character

Put the specific character directly in the pattern string. Certain special characters must be enclosed in brackets ([ ]). For more information, see Like Operator.

The following example tests whether myString consists exactly of the single character H.
VB

Dim sMatch As Boolean = myString Like "H"

To match a character in the string expression against a wildcard character

Put a question mark (?) in the pattern string. Any valid character in this position makes a successful match.

The following example tests whether myString consists of the single character W followed by exactly two characters of any values.
VB

Dim sMatch As Boolean = myString Like "W??"

To match a character in the string expression against a list of characters

Put brackets ([ ]) in the pattern string, and inside the brackets put the list of characters. Do not separate the characters with commas or any other separator. Any single character in the list makes a successful match.

The following example tests whether myString consists of any valid character followed by exactly one of the characters A, C, or E.
VB

Dim sMatch As Boolean = myString Like "?[ACE]"

Note that this match is case-sensitive.

To match a character in the string expression against a range of characters

Put brackets ([ ]) in the pattern string, and inside the brackets put the lowest and highest characters in the range, separated by a hyphen (–). Any single character within the range makes a successful match.

The following example tests whether myString consists of the characters num followed by exactly one of the characters i, j, k, l, m, or n.
VB

Dim sMatch As Boolean = myString Like "num[i-m]"

Note that this match is case-sensitive.

Matching Empty Strings

Like treats the sequence [] as a zero-length string (""). You can use [] to test whether the entire string expression is empty, but you cannot use it to test if a particular position in the string expression is empty. If an empty position is one of the options you need to test for, you can use Like more than once.

To match a character in the string expression against a list of characters or no character

Call the Like operator twice on the same string expression, and connect the two calls with either the Or Operator or the OrElse Operator.
In the pattern string for the first Like clause, include the character list, enclosed in brackets ([ ]).
In the pattern string for the second Like clause, do not put any character at the position in question.

The following example tests the seven-digit telephone number phoneNum for exactly three numeric digits, followed by a space, a hyphen (–), a period (.), or no character at all, followed by exactly four numeric digits.
VB

Dim sMatch As Boolean = 
  (phoneNum Like "###[ -.]####") OrElse (phoneNum Like "#######")

Concatenation Operators in Visual Basic

Concatenation operators join multiple strings into a single string. There are two concatenation operators, + and &. Both carry out the basic concatenation operation, as the following example shows.

Dim x As String = "Mic" & "ro" & "soft" 
Dim y As String = "Mic" + "ro" + "soft" 
' The preceding statements set both x and y to "Microsoft".

These operators can also concatenate String variables, as the following example shows.

Dim a As String = "abc"
Dim d As String = "def"
Dim z As String = a & d
Dim w As String = a + d
' The preceding statements set both z and w to "abcdef".

Differences Between the Two Concatenation Operators

The + Operator has the primary purpose of adding two numbers. However, it can also concatenate numeric operands with string operands. The + operator has a complex set of rules that determine whether to add, concatenate, signal a compiler error, or throw a run-time InvalidCastException exception.

The & Operator is defined only for String operands, and it always widens its operands to String, regardless of the setting of Option Strict. The & operator is recommended for string concatenation because it is defined exclusively for strings and reduces your chances of generating an unintended conversion.

Performance: String and StringBuilder

If you do a significant number of manipulations on a string, such as concatenations, deletions, and replacements, your performance might profit from the StringBuilder class in the System.Text namespace. It takes an extra instruction to create and initialize a StringBuilder object, and another instruction to convert its final value to a String, but you might recover this time because StringBuilder can perform faster.

Logical and Bitwise Operators in Visual Basic

Logical operators compare Boolean expressions and return a Boolean result. The And, Or, AndAlso, OrElse, and Xor operators are binary because they take two operands, while the Not operator is unary because it takes a single operand. Some of these operators can also perform bitwise logical operations on integral values.

Unary Logical Operator

The Not Operator performs logical negation on a Boolean expression. It yields the logical opposite of its operand. If the expression evaluates to True, then Not returns False; if the expression evaluates to False, then Not returns True. The following example illustrates this.

Dim x, y As Boolean
x = Not 23 > 14
y = Not 23 > 67
' The preceding statements set x to False and y to True.

Binary Logical Operators

The And Operator performs logical conjunction on two Boolean expressions. If both expressions evaluate to True, then And returns True. If at least one of the expressions evaluates to False, then And returns False.

The Or Operator performs logical disjunction or inclusion on two Boolean expressions. If either expression evaluates to True, or both evaluate to True, then Or returns True. If neither expression evaluates to True, Or returns False.

The Xor Operator performs logical exclusion on two Boolean expressions. If exactly one expression evaluates to True, but not both, Xor returns True. If both expressions evaluate to True or both evaluate to False, Xor returns False.

The following example illustrates the And, Or, and Xor operators.

Dim a, b, c, d, e, f, g As Boolean

a = 23 > 14 And 11 > 8
b = 14 > 23 And 11 > 8
' The preceding statements set a to True and b to False.

c = 23 > 14 Or 8 > 11
d = 23 > 67 Or 8 > 11
' The preceding statements set c to True and d to False.

e = 23 > 67 Xor 11 > 8
f = 23 > 14 Xor 11 > 8
g = 14 > 23 Xor 8 > 11
' The preceding statements set e to True, f to False, and g to False.

Short-Circuiting Logical Operations

The AndAlso Operator is very similar to the And operator, in that it also performs logical conjunction on two Boolean expressions. The key difference between the two is that AndAlso exhibits short-circuiting behavior. If the first expression in an AndAlso expression evaluates to False, then the second expression is not evaluated because it cannot alter the final result, and AndAlso returns False.

Similarly, the OrElse Operator performs short-circuiting logical disjunction on two Boolean expressions. If the first expression in an OrElse expression evaluates to True, then the second expression is not evaluated because it cannot alter the final result, and OrElse returns True.

Short-Circuiting Trade-Offs

Short-circuiting can improve performance by not evaluating an expression that cannot alter the result of the logical operation. However, if that expression performs additional actions, short-circuiting skips those actions. For example, if the expression includes a call to a Function procedure, that procedure is not called if the expression is short-circuited, and any additional code contained in the Function does not run. Therefore, the function might run only occasionally, and might not be tested correctly. Or the program logic might depend on the code in the Function.

The following example illustrates the difference between And, Or, and their short-circuiting counterparts.

Dim amount As Integer = 12
Dim highestAllowed As Integer = 45
Dim grandTotal As Integer

If amount > highestAllowed And checkIfValid(amount) Then
    ' The preceding statement calls checkIfValid().
End If
If amount > highestAllowed AndAlso checkIfValid(amount) Then
    ' The preceding statement does not call checkIfValid().
End If
If amount < highestAllowed Or checkIfValid(amount) Then
    ' The preceding statement calls checkIfValid().
End If
If amount < highestAllowed OrElse checkIfValid(amount) Then
    ' The preceding statement does not call checkIfValid().
End If

Function checkIfValid(ByVal checkValue As Integer) As Boolean
    If checkValue > 15 Then
        MsgBox(CStr(checkValue) & " is not a valid value.")
        ' The MsgBox warning is not displayed if the call to
        ' checkIfValid() is part of a short-circuited expression.
        Return False
    Else
        grandTotal += checkValue
        ' The grandTotal value is not updated if the call to
        ' checkIfValid() is part of a short-circuited expression.
        Return True
    End If
End Function

In the preceding example, note that some important code inside checkIfValid() does not run when the call is short-circuited. The first If statement calls checkIfValid() even though 12 > 45 returns False, because And does not short-circuit. The second If statement does not call checkIfValid(), because when 12 > 45 returns False, AndAlso short-circuits the second expression. The third If statement calls checkIfValid() even though 12 < 45 returns True, because Or does not short-circuit. The fourth If statement does not call checkIfValid(), because when 12 < 45 returns True, OrElse short-circuits the second expression.

Bitwise Operations

Bitwise operations evaluate two integral values in binary (base 2) form. They compare the bits at corresponding positions and then assign values based on the comparison. The following example illustrates the And operator.

Dim x As Integer
x = 3 And 5

The preceding example sets the value of x to 1. This happens for the following reasons:

The values are treated as binary:

3 in binary form = 011

5 in binary form = 101
The And operator compares the binary representations, one binary position (bit) at a time. If both bits at a given position are 1, then a 1 is placed in that position in the result. If either bit is 0, then a 0 is placed in that position in the result. In the preceding example this works out as follows:

011 (3 in binary form)

101 (5 in binary form)

001 (The result, in binary form)
The result is treated as decimal. The value 001 is the binary representation of 1, so x = 1.

The bitwise Or operation is similar, except that a 1 is assigned to the result bit if either or both of the compared bits is 1. Xor assigns a 1 to the result bit if exactly one of the compared bits (not both) is 1. Not takes a single operand and inverts all the bits, including the sign bit, and assigns that value to the result. This means that for signed positive numbers, Not always returns a negative value, and for negative numbers, Not always returns a positive or zero value.

The AndAlso and OrElse operators do not support bitwise operations.

Note

Bitwise operations can be performed on integral types only. Floating-point values must be converted to integral types before bitwise operation can proceed.

Efficient Combination of Operators

Complex expressions can contain many different operators. The following example illustrates this.

x = (45 * (y + z)) ^ (2 / 85) * 5 + z

Creating complex expressions such as the one in the preceding example requires a thorough understanding of the rules of operator precedence. For more information, see Operator Precedence in Visual Basic.

Parenthetical Expressions

Often you want operations to proceed in a different order from that determined by operator precedence. Consider the following example.

x = z * y + 4

The preceding example multiplies z by y, then adds the result to 4. But if you want to add y and 4 before multiplying the result by z, you can override normal operator precedence by using parentheses. By enclosing an expression in parentheses, you force that expression to be evaluated first, regardless of operator precedence. To force the preceding example to do the addition first, you could rewrite it as in the following example.

x = z * (y + 4)

The preceding example adds y and 4, then multiplies that sum by z.

Nested Parenthetical Expressions

You can nest expressions in multiple levels of parentheses to override precedence even further. The expressions most deeply nested in parentheses are evaluated first, followed by the next most deeply nested, and so on to the least deeply nested, and finally the expressions outside parentheses. The following example illustrates this.

x = (z * 4) ^ (y * (z + 2))

In the preceding example, z + 2 is evaluated first, then the other parenthetical expressions. Exponentiation, which normally has higher precedence than addition or multiplication, is evaluated last in this example because the other expressions are enclosed in parentheses.

How to: Calculate Numeric Values

You can calculate numeric values through the use of numeric expressions. A numeric expression is an expression that contains literals, constants, and variables representing numeric values, and operators that act on those values.

Calculating Numeric Values

To calculate a numeric value

Combine one or more numeric literals, constants, and variables into a numeric expression. The following example shows some valid numeric expressions.

93.217

System.Math.PI

counter

4 * (67 + i)

The first three lines show a literal, a constant, and a variable. Each one forms a valid numeric expression by itself. The final line shows a combination of a variable with two literals.

Note that a numeric expression does not form a complete Visual Basic statement by itself. You must use the expression as part of a complete statement.

To store a numeric value

You can use an assignment statement to assign the value represented by a numeric expression to a variable, as the following example demonstrates.
VB

```
Dim i As Integer = 2
Dim j As Integer
j = 4 * (67 + i)
```
In the preceding example, the value of the expression on the right side of the equal operator (=) is assigned to the variable j on the left side of the operator, so j evaluates to 276.

For more information, see Statements.

Multiple Operators

If the numeric expression contains more than one operator, the order in which they are evaluated is determined by the rules of operator precedence. To override the rules of operator precedence, you enclose expressions in parentheses, as in the above example; the enclosed expressions are evaluated first.

To override normal operator precedence

Use parentheses to enclose the operations you want to be performed first. The following example shows two different results with the same operands and operators.
VB

```
Dim i As Integer = 2
Dim j, k As Integer
j = 4 * (67 + i)
k = 4 * 67 + i
```
In the preceding example, the calculation for j performs the addition operator (+) first because the parentheses around (67 + i) override normal precedence, and the value assigned to j is 276 (4 times 69). The calculation for k performs the operators in their normal precedence (* before +), and the value assigned to k is 270 (268 plus 2).

For more information, see Operator Precedence in Visual Basic.

Value Comparisons

Comparison operators can be used to construct expressions that compare the values of numeric variables. These expressions return a Boolean value based on whether the comparison is true or false. Examples of such an expression are as follows.

45 > 26

26 > 45

The first expression evaluates to True, because 45 is greater than 26. The second example evaluates to False, because 26 is not greater than 45.

You can also compare numeric expressions in this fashion. The expressions you compare can themselves be complex expressions, as in the following example.

x / 45 * (y +17) >= System.Math.Sqrt(z) / (p - (x * 16))

The preceding complex expression includes literals, variables, and function calls. The expressions on both sides of the comparison operator are evaluated, and the resulting values are then compared using the >= comparison operator. If the value of the expression on the left side is greater than or equal to the value of the expression on the right, the entire expression evaluates to True; otherwise, it evaluates to False.

Expressions that compare values are most commonly used in If...Then constructions, as in the following example.

If x > 50 Then
    ' Insert code to run if x is greater than 50.
Else
    ' Insert code to run if x is less than or equal to 50.
End If

The = sign is a comparison operator as well as an assignment operator. When used as a comparison operator, it evaluates whether the value on the left is equal to the value on the right, as shown in the following example.

If x = 50 Then
    ' Insert code to continue program.
End If

You can also use a comparison expression anywhere a Boolean value is needed, such as in an If, While, Loop, or ElseIf statement, or when assigning to or passing a value to a Boolean variable. In the following example, the value returned by the comparison expression is assigned to a Boolean variable.

Dim x As Boolean
x = 50 < 30
' The preceding statement assigns False to x.

Boolean Expressions

A Boolean expression is an expression that evaluates to a value of the Boolean Data Type: True or False. Boolean expressions can take several forms. The simplest is the direct comparison of the value of a Boolean variable to a Boolean literal, as shown in the following example.

If newCustomer = True Then
    ' Insert code to execute if newCustomer = True.
Else
    ' Insert code to execute if newCustomer = False.
End If

Two Meanings of the = Operator

Notice that the assignment statement newCustomer = True looks the same as the expression in the preceding example, but it performs a different function and is used differently. In the preceding example, the expression newCustomer = True represents a Boolean value, and the = sign is interpreted as a comparison operator. In a stand-alone statement, the = sign is interpreted as an assignment operator and assigns the value on the right to the variable on the left. The following example illustrates this.

If newCustomer = True Then
    newCustomer = False
End If

For further information, see Value Comparisons and Statements.

Comparison Operators

Comparison operators such as =, <, >, <>, <=, and >= produce Boolean expressions by comparing the expression on the left side of the operator to the expression on the right side of the operator and evaluating the result as True or False. The following example illustrates this.

42 < 81

Because 42 is less than 81, the Boolean expression in the preceding example evaluates to True. For more information on this kind of expression, see Value Comparisons.

Comparison Operators Combined with Logical Operators

Comparison expressions can be combined using logical operators to produce more complex Boolean expressions. The following example demonstrates the use of comparison operators in conjunction with a logical operator.

x > y And x < 1000

In the preceding example, the value of the overall expression depends on the values of the expressions on each side of the And operator. If both expressions are True, then the overall expression evaluates to True. If either expression is False, then the entire expression evaluates to False.

Short-Circuiting Operators

The logical operators AndAlso and OrElse exhibit behavior known as short-circuiting. A short-circuiting operator evaluates the left operand first. If the left operand determines the value of the entire expression, then program execution proceeds without evaluating the right expression. The following example illustrates this.

If 45 < 12 AndAlso testFunction(3) = 81 Then
    ' Add code to continue execution.
End If

In the preceding example, the operator evaluates the left expression, 45 < 12. Because the left expression evaluates to False, the entire logical expression must evaluate to False. Program execution thus skips execution of the code within the If block without evaluating the right expression, testFunction(3). This example does not call testFunction() because the left expression falsifies the entire expression.

Similarly, if the left expression in a logical expression using OrElse evaluates to True, execution proceeds to the next line of code without evaluating the right expression, because the left expression has already validated the entire expression.

Comparison with Non-Short-Circuiting Operators

By contrast, both sides of the logical operator are evaluated when the logical operators And and Or are used. The following example illustrates this.

If 45 < 12 And testFunction(3) = 81 Then
    ' Add code to continue execution.
End If

The preceding example calls testFunction() even though the left expression evaluates to False.

Parenthetical Expressions

You can use parentheses to control the order of evaluation of Boolean expressions. Expressions enclosed by parentheses evaluate first. For multiple levels of nesting, precedence is granted to the most deeply nested expressions. Within parentheses, evaluation proceeds according to the rules of operator precedence. For more information, see Operator Precedence in Visual Basic.

Content

VB.NET Operators and Expressions

Types of Operators

Evaluation of Expressions

See also

Common Tasks Performed with Visual Basic Operators

Arithmetic and Bit-shift Tasks

Comparison Tasks

Concatenation Tasks

Logical and Bitwise Tasks

See also

Arithmetic Operators in Visual Basic

Arithmetic Operations

Attempted Division by Zero

Bit-Shift Operations

Bitwise Operations

Type Safety

See also

Comparison Operators in Visual Basic

Comparing Numeric Values

Comparing Strings

Comparing Objects

Comparing Object Type

See also

How to: Test Whether Two Objects Are the Same

To test whether two objects are the same

See also

How to: Match a String against a Pattern

To match a character in the string expression against a specific character

To match a character in the string expression against a wildcard character

To match a character in the string expression against a list of characters

To match a character in the string expression against a range of characters

Matching Empty Strings

To match a character in the string expression against a list of characters or no character

See also

Concatenation Operators in Visual Basic

Differences Between the Two Concatenation Operators

Performance: String and StringBuilder

See also

Logical and Bitwise Operators in Visual Basic

Unary Logical Operator

Binary Logical Operators

Short-Circuiting Logical Operations

Short-Circuiting Trade-Offs

Bitwise Operations

See also

Efficient Combination of Operators

Parenthetical Expressions

Nested Parenthetical Expressions

See also

How to: Calculate Numeric Values

Calculating Numeric Values

To calculate a numeric value

To store a numeric value

Multiple Operators

To override normal operator precedence

See also

Value Comparisons

See also

Boolean Expressions

Two Meanings of the = Operator

Comparison Operators

Comparison Operators Combined with Logical Operators

Short-Circuiting Operators

Comparison with Non-Short-Circuiting Operators

Parenthetical Expressions

See also

Source/Reference