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Programming Logic: Execute code based on conditions

The If Condition

VB lets you execute code based on conditions.

To test a condition you use the if statement. The if statement returns true or false, based on your test:

  • The if statement starts a code block
  • The condition is written between if and then
  • The code between if ... then and end if is executed if the test is true

    • Example

    @Code
    Dim price=50
    End Code
    <html>
    <body>
    @If price>30 Then
        @<p>The price is too high.</p>
    End If
    </body>
    </html>

    The Else Condition

    An if statement can include an else condition.

    The else condition defines the code to be executed if the condition is false.

    Example

    @Code
    Dim price=20
    End Code
    <html>
    <body>
    @if price>30 then
        @<p>The price is too high.</p>
    Else
        @<p>The price is OK.</p>
    End If
    </body>
    </html>
    Note: In the example above, if the first condition is true, it will be executed. The else condition covers "everything else".

    The ElseIf Condition

    Multiple conditions can be tested with an else if condition:

    Example

    @Code
    Dim price=25
    End Code
    <html>
    <body>
    @If price>=30 Then
        @<p>The price is high.</p>
    ElseIf price>20 And price<30 then
        @<p>The price is OK.</p>
    Else
        @<p>The price is low.</p>
    End If   
    </body>
    </html>

    In the example above, if the first condition is true, it will be executed.

    If not, then if the next condition is true, this condition will be executed.

    You can have any number of else if conditions.

    If none of the if or else if conditions are true, the last else block (without a condition) covers "everything else".

    Select Conditions

    A select block can be used to test a number of individual conditions:

    Example

    @Code
    Dim weekday=DateTime.Now.DayOfWeek
    Dim day=weekday.ToString()
    Dim message=""
    End Code
    <html>
    <body>
    @Select Case day
    Case "Monday"
        message="This is the first weekday."
    Case "Thursday"
        message="Only one day before weekend."
    Case "Friday"
        message="Tomorrow is weekend!"
    Case Else
        message="Today is " & day
    End Select
    <p>@message</p>
    </body>
    </html>

    "Select Case" is followed by the test value (day). Each individual test condition has a case value, and any number of code lines. If the test value matches the case value, the code lines are executed.

    A select block can have a default case (Case Else) for "everything else" that runs if none of the other cases are true.

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