Contents
In this document we will show some statements that provide
a way to control the program flow that means to influence the
sequence of source code statements that will be executed. Other methods to
change the execution order like subroutine calls or event handling will be
described in other documents.
Executes a group of statements conditionally. The result
value of an expression defines if the sattements behind the
Then or the statements behind the Else will be executed.
Syntax
If condition Then
[statements1]
[ Else If
[statements2]]
[Else
[statements3]]
End If
where condition is a numeric expression that evaluates to True
or False.
statements are one or more statements that are executed if the
result of the condition is True.
If example
This example prints some text dpending on
the value of the variable i.
' Event handler for button_click event
Sub btn_start_clicked()
Dim i As Integer
i = 9
Print "Value is "+str(i)
If i < 5 Then
Print "Less than 5"
Else
Print "Greater than 5"
End If
If i < 10 Then
Print "Less than 10"
Else
Print "Greater then 10"
End If
End Sub
|
Example ex_if.bas: Example how to use the if statement.
See Also
Select...Case statement
Executes a group of statements while a condition is
True .
Syntax
While condition [Do]
[statements]
Wend
where condition is a numeric expression with value True or False.
statements are one or more statements executed while condition
is True.
While loop
This example shows how to use the While..Wend statement.
' While..Do loop example
Sub btn_start_clicked()
Dim i As Integer
i = 1
While i < 5
Print i
i = i + 1
Wend
Print "New loop"
While i <= 10 Do
Print i
i = i + 1
Wend
End Sub
|
Example ex_while.bas: Example of while loop statement
See Also
Do...Loop Statement
Repeat a group of statements a specified number of times
Syntax
For counter = start_value To end_value [ Step
step_value ]
[statements]
Next counter
where counter is a numerical variable which may be defined in a
Dim Statement
start_value is the initial value of the loop variable
end_value is the final value of the loop variable
step_value is the value the counter will be changed each time through
the loop
statements are one or more statements that are executed a specified
number of times.
Example
This example shows a simple for-loop.
' For loop
Sub btn_start_clicked()
Dim i As Integer
For i = 1 To 5
Print "Value = "+str(i)
Next i
For i = 3 To 15 Step 3
Print i
Next i
End Sub
|
Example ex_for.bas: Example of For..Next statement.
See Also
Do...Loop Statement , While...Wend Statement
|
Do..Loop and Exit statement
|
The Do..Loop statement repeates a block of statements
until the Exit statement will be called to terminate the loop.
' Do..Loop with exit termination
Sub btn_start_clicked()
Dim i As Integer
i = 1
Do
If i > 10 Then
Exit Do
End If
Print i
i = i + 1
Loop
End Sub
|
Example ex_doloop.bas: Show of Do..Loop statement
Exit statement
Provides a way to exit a Do...Loop statement.
Exit Do transfers control to the statement immediatly following
the Loop statement. It can be used only inside a Do...Loop statement.
When used within nested Do..Loop statements, Exit Do transfers control
to the loop that is the one nested level above the loop where Exit
Loop occurs.
See also
End Statement, Do...Loop While
and Do..Loop Until
Statement
|
Do..While / Until-Loop statement
|
The Do-Loop structure repeats a block of statements.
The statements in the body of the structure may be repeated while
a condition becomes tru or until a condition becomes true.
Any number of Exit Do statements may be placed anywhere
in the Do...Loop structure as an alternate way to exit.
If the running program reaches the Exit Loop statement
control is transfered to the statement immediately following the
Loop .
When used within nested Do..Loop statements, Exit Do transfers control
to the loop that is the one nested level above the loop where
Exit Loop occurs.
Syntax
Do [{While | Until} condition ]
[statements]
[Exit Do]
[statements]
Loop
or
Do
[statements]
[Exit Do]
[statements]
Loop [{While | Until }] condition ]
where condition is a numeric expression with result True or False
and
statements are one or more statements that are repeated while or
until condition is True.
Example
This example shows how Do..Loop statements can be
used. The loop counts from 1 to 10 and prints the current value
in the form.
Do..While example
The select example selects all rows from the table
tab1 and prints the value of column col1 for each row.
' While..Do..While loop example
Sub btn_start_clicked()
Dim i As Integer
i = 1
Do While i <= 5
Print i
i = i + 1
Loop
i = i + 2
Print "New loop"
Do
Print i
i = i + 1
Loop While i <= 10
End Sub
|
Example ex_while_do.bas: Example of while..do statement
Do..Until
The select example selects all rows from the table
tab1 and prints the value of column col1 for each row.
' Until..Do..Until loop example
Sub btn_start_clicked()
Dim i As Integer
i = 1
Do Until i > 5
Print i
i = i + 1
Loop
i = i + 2
Print "New loop"
Do
Print i
i = i + 1
Loop Until i > 10
End Sub
|
Example ex_until_do.bas: Example of the Do..Until statement.
See also
Exit Statement, For...Next Statement,
While...Wend Statement
Executes a group of statements depending on the
value of an expression.
Syntax
Select Case sel_expression
[Case expression_1
[statements_1]] ...
[Case expression_n
[statements_n]]
[Case Else
[statements_else]]
End Select
where sel_expression is a numeric expression which leads to a compare_value
expression_i is a numeric expression which is compared to the compare_value.
If the values are eual the following statements will be executed.
statements_i are one or more statements that will be executed if
the depending expression is equal to the compare_value.
Example
This example should show the text "select 2" selected
by the value of 'i'.
' Select..case program example
Public i As Integer
Sub btn_start_clicked()
i = 2
Select Case i
Case 1
Print "select 1"
Case 2
Print "select 2"
Case Else
Print "Other value"
End Select
End Sub
|
Example ex_select_case.bas: Example of Select..Case statement
See Also
If...Then...Else Statement