If...Then...Else Statement (Visual Basic)
Conditionally executes a group of statements, depending on the value of an expression.
Syntax
' Multiline syntax:
If condition [ Then ]
[ statements ]
[ ElseIf elseifcondition [ Then ]
[ elseifstatements ] ]
[ Else
[ elsestatements ] ]
End If
' Single-line syntax:
If condition Then [ statements ] [ Else [ elsestatements ] ]
Quick links to example code
This article includes several examples that illustrate uses of the If...Then...Else statement:
Parts
condition
Required. Expression. Must evaluate to True or False, or to a data type that is implicitly convertible to Boolean.
If the expression is a Nullable Boolean variable that evaluates to Nothing, the condition is treated as if the expression is False, and the ElseIf blocks are evaluated if they exist, or the Else block is executed if it exists.
Then
Required in the single-line syntax; optional in the multiline syntax.
statements
Optional. One or more statements following If...Then that are executed if condition evaluates to True.
elseifcondition
Required if ElseIf is present. Expression. Must evaluate to True or False, or to a data type that is implicitly convertible to Boolean.
elseifstatements
Optional. One or more statements following ElseIf...Then that are executed if elseifcondition evaluates to True.
elsestatements
Optional. One or more statements that are executed if no previous condition or elseifcondition expression evaluates to True.
End If
Terminates the multiline version of If...Then...Else block.
Remarks
Multiline syntax
When an If...Then...Else statement is encountered, condition is tested. If condition is True, the statements following Then are executed. If condition is False, each ElseIf statement (if there are any) is evaluated in order. When a True elseifcondition is found, the statements immediately following the associated ElseIf are executed. If no elseifcondition evaluates to True, or if there are no ElseIf statements, the statements following Else are executed. After executing the statements following Then, ElseIf, or Else, execution continues with the statement following End If.
The ElseIf and Else clauses are both optional. You can have as many ElseIf clauses as you want in an If...Then...Else statement, but no ElseIf clause can appear after an Else clause. If...Then...Else statements can be nested within each other.
In the multiline syntax, the If statement must be the only statement on the first line. The ElseIf, Else, and End If statements can be preceded only by a line label. The If...Then...Else block must end with an End If statement.
Tip
The Select...Case Statement might be more useful when you evaluate a single expression that has several possible values.
Single-Line syntax
You can use the single-line syntax for a single condition with code to execute if it's true. However, the multiple-line syntax provides more structure and flexibility and is easier to read, maintain, and debug.
What follows the Then keyword is examined to determine whether a statement is a single-line If. If anything other than a comment appears after Then on the same line, the statement is treated as a single-line If statement. If Then is absent, it must be the start of a multiple-line If...Then...Else.
In the single-line syntax, you can have multiple statements executed as the result of an If...Then decision. All statements must be on the same line and be separated by colons.
Multiline syntax example
The following example illustrates the use of the multiline syntax of the If...Then...Else statement.
'Create a Random object to seed our starting value
Dim randomizer As New Random()
'set our variable
Dim count As Integer = randomizer.Next(0, 5)
Dim message As String
'If count is zero, output will be no items
If count = 0 Then
message = "There are no items."
'If count is 1, output will be "There is 1 item.".
ElseIf count = 1 Then
message = "There is 1 item."
'If count is greater than 1, output will be "There are {count} items.", where {count} is replaced by the value of count.
Else
message = $"There are {count} items."
End If
Console.WriteLine(message)
'This example displays output like the following:
' There are 4 items.
Nested syntax example
The following example contains nested If...Then...Else statements.
Public Sub Main()
' Run the function as part of the WriteLine output.
Console.WriteLine("Time Check is " & CheckIfTime() & ".")
End Sub
Private Function CheckIfTime() As Boolean
' Determine the current day of week and hour of day.
Dim dayW As DayOfWeek = DateTime.Now.DayOfWeek
Dim hour As Integer = DateTime.Now.Hour
' Return True if Wednesday from 2 to 3:59 P.M.,
' or if Thursday from noon to 12:59 P.M.
If dayW = DayOfWeek.Wednesday Then
If hour = 14 Or hour = 15 Then
Return True
Else
Return False
End If
ElseIf dayW = DayOfWeek.Thursday Then
If hour = 12 Then
Return True
Else
Return False
End If
Else
Return False
End If
End Function
'This example displays output like the following:
'Time Check is False.
Single-Line syntax example
The following example illustrates the use of the single-line syntax.
Private Sub SingleLine()
'Create a Random object to seed our starting values
Dim randomizer As New Random()
Dim A As Integer = randomizer.Next(10, 20)
Dim B As Integer = randomizer.Next(0, 20)
Dim C As Integer = randomizer.Next(0, 5)
'Let's display the initial values for comparison
Console.WriteLine($"A value before If: {A}")
Console.WriteLine($"B value before If: {B}")
Console.WriteLine($"C value before If: {C}")
' If A > 10, execute the three colon-separated statements in the order
' that they appear
If A > 10 Then A = A + 1 : B = B + A : C = C + B
'If the condition is true, the values will be different
Console.WriteLine($"A value after If: {A}")
Console.WriteLine($"B value after If: {B}")
Console.WriteLine($"C value after If: {C}")
End Sub
'This example displays output like the following:
'A value before If: 11
'B value before If: 6
'C value before If: 3
'A value after If: 12
'B value after If: 18
'C value after If: 21
