Question

In this part of the Visual Basic tutorial, we will talk about operators.

An operator is a special symbol which indicates a certain process is carried out. Operators in programming languages are taken from mathematics. Programmers work with data. The operators are used to process data.

We have several types of operators:

• Arithmetic operators
• Boolean operators
• Relational operators
• Bitwise operators

An operator may have one or two operands. An operand is one of the inputs (arguments) of an operator. Those operators that work with only one operand are called unary operators. Those who work with two operands are called binary operators.

Option Strict On

Module Example

  Sub Main()

    Console.WriteLine(2)
    Console.WriteLine(-2)
    Console.WriteLine(2+2)
    Console.WriteLine(2-2)

  End Sub

End Module

The + and - signs can be addition and subtraction operators as well as unary sign operators. It depends on the situation.

Option Strict On

Module Example

  Dim a As Byte

  Sub Main()

    a = 1
    Console.WriteLine(-a)  ' Prints -1
    Console.WriteLine(-(-a)) ' Prints 1

  End Sub

End Module

The plus sign can be used to indicate that we have a positive number. But it is mostly not used. The minus sign changes the sign of a value.

Option Strict On


Module Example

  Dim a As Byte
  Dim b As Byte

  Sub Main()

    a = 3 * 3
    b = 2 + 2   
    
    Console.WriteLine(a) ' Prints 9
    Console.WriteLine(b) ' Print 4

  End Sub

End Module

Multiplication and addition operators are examples of binary operators. They are used with two operands.

The assignment operator

The assignment operator = assigns a value to a variable. A variable is a placeholder for a value. In mathematics, the = operator has a different meaning. In an equation, the = operator is an equality operator. The left side of the equation is equal to the right one.

x = 1
Console.WriteLine(x) ' Prints 1

Here we assign a number to the x variable.

x = x + 1
Console.WriteLine(x)

The previous expression does not make sense in mathematics. But it is legal in programming. The expression adds 1 to the x variable. The right side is equal to 2 and 2 is assigned to x .

3 = x

This code example results in syntax error. We cannot assign a value to a literal.

Arithmetic operators

The following is a table of arithmetic operators in Visual Basic.

Symbol	Name
+	Addition
-	Subtraction
*	Multiplication
/	Division
\	Integer Division
Mod	Modulo
^	Exponentiation

The following example shows arithmetic operations.

Option Strict On


Module Example

  Dim a As Byte
  Dim b As Byte
  Dim c As Byte

  Dim add As Byte
  Dim sb As Byte
  Dim mult As Byte
  Dim div As Byte

  Sub Main()

    a = 10
    b = 11
    c = 12

    add = a + b + c
    sb = c - a
    mult = a * b
    div = CType(c / 3, Byte)
    
    Console.WriteLine(add)
    Console.WriteLine(sb)
    Console.WriteLine(mult)
    Console.WriteLine(div)

  End Sub

End Module

In the preceding example, we use addition, subtraction, multiplication and division operations. This is all familiar from the mathematics.

$ ./arithmetic.exe 
33
2
110
4

Output of the example.

Next we will show the distinction between normal and integer division.

Option Strict On


Module Example

  Dim a As Single = 5
  Dim b As Single = 2
  Dim c As Single

  Sub Main()

    c = 5 / 2 
    Console.WriteLine(c)
    c = 5 \ 2
    Console.WriteLine(c)
    
  End Sub

End Module

In the preceding example, we divide two numbers using normal and integer division operator. Visual Basic has two distinct operators for division.

Dim a As Single = 5

We use floating point data types.

c = 5 / 2 
Console.WriteLine(c)

This is the 'normal' division operation. It returns 2.5, as expected.

c = 5 \ 2
Console.WriteLine(c)

This is integer division. The result of this operation is always and integer. The c variable has value 2.

$ ./division.exe 
2.5
2

Result of the division.exe program.

The last two operators that we will mention are modulo operator and exponentiation operator.

Console.WriteLine(9 Mod 4) ' Prints 1

The Mod operator is called the modulo operator. It finds the remainder of division of one number by another. 9 Mod 4 , 9 modulo 4 is 1, because 4 goes into 9 twice with a remainder of 1. Modulo operator can be handy for example when we want to check for prime numbers.

Finally, we will mention exponentiation operator.

Console.WriteLine(9 ^ 2) ' Prints 81

9 ^ 2 = 9 * 9 = 81

Concatenating strings

In Visual Basic we have two operators for string concatenation. The plus + operator and the & ampersand operator.

Option Strict On


Module Example

  Sub Main()

    Console.WriteLine("Return " & "of " & "the king")
    Console.WriteLine("Return " + "of " + "the king")

  End Sub

End Module

We join three strings together using both operators.

$ ./concatstrings.exe 
Return of the king
Return of the king

And this is, what we get. Same result for both cases.

Boolean operators

In Visual Basic, we have the following logical operators. Boolean operators are also called logical.

Symbol	Name
And	logical conjunction
AndAlso	short circuit And
Or	logical inclusion
OrElse	short circuit Or
Xor	logical inclusion
Not	negation

Boolean operators are used to work with truth values.

Option Strict On


Module Example

  Dim x As Byte = 3
  Dim y As Byte = 8

  Sub Main()

    Console.WriteLine(x = y) 
    Console.WriteLine(y > x)

    If (y > x)
      Console.WriteLine("y is greater than x")
    End If

  End Sub

End Module

Many expressions result in a boolean value. Boolean values are used in conditional statements.

Console.WriteLine(x = y) 
Console.WriteLine(y > x)

Relational operators always result in a Boolean value. These two lines print False and True.

If (y > x)
  Console.WriteLine("y is greater than x")
End If

The body of the If statement is executed only if the condition inside the parentheses is met. The x > y returns True, so the message "y is greater than x" is printed to the terminal.

Option Strict On


Module Example

  Dim a As Boolean
  Dim b As Boolean
  Dim c As Boolean
  Dim d As Boolean

  Sub Main()

    a = (True And True)
    b = (True And False)
    c = (False And True)
    d = (False And False)

    Console.WriteLine(a)
    Console.WriteLine(b)
    Console.WriteLine(c)
    Console.WriteLine(d)


  End Sub

End Module

Example shows the logical And operator. It evaluates to True only if both operands are True.

$ ./andop.exe 
True
False
False
False

The logical Xor operator evaluates to True, if exactly one of the operands is True.

Option Strict On


Module Example

  Dim a As Boolean
  Dim b As Boolean
  Dim c As Boolean
  Dim d As Boolean

  Sub Main

    a = (True Xor True)
    b = (True Xor False)
    c = (False Xor True)
    d = (False Xor False)

    Console.WriteLine(a)
    Console.WriteLine(b)
    Console.WriteLine(c)
    Console.WriteLine(d)

  End Sub

End Module

The logical Xor evaluates to False if both operands are True or both False.

$ ./xorop.exe 
False
True
True
False

The logical Or operator evaluates to True, if either of the operands is True.

Option Strict On


Module Example

  Sub Main()

    Dim a As Boolean = True Or True
    Dim b As Boolean = True Or False
    Dim c As Boolean = False Or True
    Dim d As Boolean = False Or False

    Console.WriteLine(a)
    Console.WriteLine(b)
    Console.WriteLine(c)
    Console.WriteLine(d)

  End Sub

End Module

If one of the sides of the operator is True, the outcome of the operation is True.

$ ./orop.exe 
True
True
True
False

The negation operator Not makes True False and False True.

Option Strict On


Module Example

  Sub Main()

    Console.WriteLine(Not True)
    Console.WriteLine(Not False)
    Console.WriteLine(Not (4 < 3))

  End Sub

End Module

The example shows the negation operator in action.

$ ./negation.exe 
False
True
True

AndAlso , OrElse operators are short circuit evaluated. Short circuit evaluation means that the second argument is only evaluated if the first argument does not suffice to determine the value of the expression: when the first argument of And evaluates to false, the overall value must be false; and when the first argument of Or evaluates to true, the overall value must be true. (wikipedia) Short circuit evaluation is used mainly to improve performance.

An example may clarify this a bit more.

Option Strict On


Module Example

  Sub Main()

    Console.WriteLine("Short circuit")
    If (one AndAlso two)
      Console.WriteLine("Pass")
    End If

    Console.WriteLine("#############")
    If (one And two)
      Console.WriteLine("Pass")
    End If

  End Sub

Function one As Boolean
  Console.WriteLine("Inside one")
  Return False
End Function

Function two As Boolean
  Console.WriteLine("Inside two")
  Return True
End Function

End Module

We have two functions in the example. Functions, unlike subroutines, return values. This is the main difference between them.

If (one AndAlso two)
  Console.WriteLine("Pass")
End If

The one function returns False. The short circuit AndAlso does not evaluate the second function. It is not necessary. Once an operand is False, the result of the logical conclusion is always False. Only "Inside one" is printed to the console.

Console.WriteLine("#############")
If (one And two)
  Console.WriteLine("Pass")
End If

In the second case, we use the And . In this case, both functions are called. Even though it is not necessary for the result of the expression.

$ ./shorcircuit.exe 
Short circuit
Inside one
#############
Inside one
Inside two

Result of the shorcircuit.exe program.

Relational Operators

Relational operators are used to compare values. These operators always result in a boolean value.

Symbol	Meaning
<	less than
<=	less than or equal to
>	greater than
>=	greater than or equal to
==	equal to
<>	not equal to
Is	compares references

Relational operators are also called comparison operators.

Console.WriteLine(3 < 4) ' Prints True
Console.WriteLine(3 = 4) ' Prints False
Console.WriteLine(4 >= 3) ' Prints True

As we already mentioned, the relational operators return boolean values. Note that in Visual Basic, the comparison operator is = . Not == like in C and C influenced languages.

Notice that the relational operators are not limited to numbers. We can use them for other objects as well. Although they might not always be meaningful.

Option Strict On


Module Example


  Sub Main()

    Console.WriteLine("six" = "six") ' Prints True
    ' Console.WriteLine("a" > 6) this would throw
                   ' an exception 
    Console.WriteLine("a" < "b") ' Prints True

  End Sub

End Module

We can compare string objects too. Comparison operators in a string context compare the sorting order of the characters.

Console.WriteLine("a" < "b") ' Prints True

What exactly happens here? Computers do not know characters or strings. For them, everything is just a number. Characters are special numbers stored in specific tables. Like ASCII.

Option Strict On

Module Example

  Sub Main()

    Console.WriteLine("a" < "b")
    
    Console.WriteLine("a is: {0}",  Asc("a"))
    Console.WriteLine("b is: {0}",  Asc("b"))
    
  End Sub

End Module

Internally, the a and b characters are numbers. So when we compare two characters, we compare their stored numbers. The built-in Asc function returns the ASCII value of a single character.

$ ./compare.exe 
True
a is: 97
b is: 98

In fact, we compare two numbers, 97 with 98.

Console.WriteLine("ab" > "aa") ' Prints True

Say we have a string with more characters. If the first characters are equal, we compare the next ones. In our case, the b character at the second position has a greater value than the a character. That is why "ab" string is greater than "aa" string. Comparing strings in such a way does not make much sense, of course. But it is technically possible.

Finally, we will mention the Is operator. The operator checks if two object references refer to the same object. It does not perform value comparisons.

Option Strict On


Module Example

  Sub Main()

    Dim o1 As Object = New Object
    Dim o2 As Object = New Object
    Dim o3 As Object 
    
    o3 = o2

    Console.WriteLine(o1 Is o2)
    Console.WriteLine(o3 Is o2)

  End Sub

End Module

We create three objects and compare them with the Is operator.

Dim o1 As Object = New Object
Dim o2 As Object = New Object

We declare and initialise two Object instances. The Object class is a base class for all classes in the .NET framework. We will describe it later in more detail.

Dim o3 As Object 

The third variable is only declared.

o3 = o2

The o3 now refers to the o2 object. They are two references to the same object.

Console.WriteLine(o1 Is o2)
Console.WriteLine(o3 Is o2)

In the first case, we get False. The o1 and o2 are two different objects. In the second case, we get True. The o3 and o2 refer to the same object.

Bitwise operators

Decimal numbers are natural to humans. Binary numbers are native to computers. Binary, octal, decimal, or hexadecimal symbols are only notations of the same number. Bitwise operators work with bits of a binary number. Bitwise operators are seldom used in higher level languages like Visual Basic.

Symbol	Meaning
Not	bitwise negation
Xor	bitwise exclusive or
And	bitwise and
Or	bitwise or

The bitwise negation operator changes each 1 to 0 and 0 to 1.

Console.WriteLine(Not 7)  ' Prints -8
Console.WriteLine(Not -8) ' Prints 7

The operator reverts all bits of a number 7. One of the bits also determines, whether the number is negative or not. If we negate all the bits one more time, we get number 7 again.

The bitwise and operator performs bit-by-bit comparison between two numbers. The result for a bit position is 1 only if both corresponding bits in the operands are 1.

    00110
  And 00011
   =  00010

The first number is a binary notation of 6, the second is 3 and the result is 2.

Console.WriteLine(6 And 3) ' Prints 2
Console.WriteLine(3 And 6) ' Prints 2

The bitwise or operator performs bit-by-bit comparison between two numbers. The result for a bit position is 1 if either of the corresponding bits in the operands is 1.

   00110
  Or 00011
   = 00111

The result is 00110 or decimal 7.

Console.WriteLine(6 Or 3) ' Prints 7
Console.WriteLine(3 Or 6) ' Prints 7

The bitwise exclusive or operator performs bit-by-bit comparison between two numbers. The result for a bit position is 1 if one or the other (but not both) of the corresponding bits in the operands is 1.

    00110
  Xor 00011
   =  00101

The result is 00101 or decimal 5.

Console.WriteLine(6 Xor 3) ' Prints 5

Compound assignment operators

The compound assignment operators consist of two operators. They are shorthand operators.

Option Strict On

Module Example

  Dim a As Integer

  Sub Main

    a = 1
    a = a + 1
    Console.WriteLine(a) ' Prints 2

    a += 1
    Console.WriteLine(a) ' Prints 3

  End Sub

End Module

The += compound operator is one of these shorthand operators. They are less readable than the full expressions but experienced programmers often use them.

Other compound operators are:

-=   *=   \=   /=   &=  ^= 

Operator precedence

The operator precedence tells us which operators are evaluated first. The precedence level is necessary to avoid ambiguity in expressions.

What is the outcome of the following expression, 28 or 40?

 3 + 5 * 5

Like in mathematics, the multiplication operator has a higher precedence than addition operator. So the outcome is 28.

(3 + 5) * 5

To change the order of evaluation, we can use parentheses. Expressions inside parentheses are always evaluated first.

The following list shows common Visual Basic operators ordered by precedence (highest precedence first):

Operator(s)	Description
^	exponentiation
+ -	unary identity and negation
* /	multiplication, float division
\	integer division
Mod	modulus
+ -	addition, subtraction, string concatenation
&	string concatenation
<< >>	arithmetic bit shift
= <> < > >= <= Is IsNot Like TypeOf Is	All comparison operators
Not	negation
And AndAlso	conjunction
Or OrElse	Inclusive disjunction
Xor	Exclusive disjunction

Operators on the same line in the list have the same precedence.

Option Strict On

Module Example

  Sub Main()

    Console.WriteLine(3 + 5 * 5)
    Console.WriteLine((3 + 5) * 5)

    Console.WriteLine(Not True Or True)
    Console.WriteLine(Not (True Or True))

  End Sub

End Module

In this code example, we show some common expressions. The outcome of each expression is dependent on the precedence level.

Console.WriteLine(3 + 5 * 5)

This line prints 28. The multiplication operator has a higher precedence than addition. First the product of 5*5 is calculated. Then 3 is added.

Console.WriteLine(Not True Or True)

In this case, the negation operator has a higher precedence. First, the first True value is negated to False, than the Or operator combines False and True, which gives True in the end.

$ ./precedence.exe 
28
40
True
False

Associativity

Sometimes the precedence is not satisfactory to determine the outcome of an expression. There is another rule called associativity. The associativity of operators determines the order of evaluation of operators with the same precedence level.

9 / 3 * 3

What is the outcome of this expression? 9 or 1? The multiplication, deletion and the modulo operator are left to right associated. So the expression is evaluated this way: (9 / 3) * 3 and the result is 9.

Arithmetic, boolean, relational and bitwise operators are all left o right associated.

On the other hand, the assignment operator is right associated.

a = b = c = d = 0
Console.WriteLine("{0} {1} {2} {3}", a, b, c, d) ' Prints 0 0 0 0 

If the association was left to right, the previous expression would not be possible.

The compound assignment operators are right to left associated.

j = 0
j *= 3 + 1
Console.WriteLine(j)  

You might expect the result to be 1. But the actual result is 0. Because of the associativity. The expression on the right is evaluated first and than the compound assignment operator is applied.

AddressOf operator

The AddressOf operator creates a function delegate that points to another function. Delegates are type safe function pointers, they are used to call methods of other objects.

Option Strict On


Module Example

  Delegate Sub Display

  Dim msg As New Display(AddressOf Message1)

  Sub Main()

    msg.Invoke()
    msg = New Display(AddressOf Message2)
    msg.Invoke()

  End Sub

  Sub Message1()
    Console.WriteLine("This is message 1")
  End Sub

  Sub Message2()
    Console.WriteLine("This is message 2")
  End Sub

End Module

In the code example, we use the AddressOf operator to point to two different subroutines.

Delegate Sub Display

We need to declare a delegate.

Dim msg As New Display(AddressOf Message1)

The delegate takes the address of a subroutine using the AddressOf operator. Now we have a type-safe pointer to the Message1() subroutine.

msg.Invoke()

The Invoke() method calls the method, to which the delegate points.

msg = New Display(AddressOf Message2)
msg.Invoke()

Now we give the delegate an address of another subroutine.

$ ./addressof.exe 
This is message 1
This is message 2

Both messages are printed to the console.

In this part of the Visual Basic tutorial, we covered the operators.