# Flow control structures
# For loop
For loop is used to repeat the enclosed section of code a given number of times. The following simple example illustrates the basic syntax:
Dim i as Integer 'Declaration of i For i = 1 to 10 'Declare how many times the loop shall be executed Debug.Print i 'The piece of code which is repeated Next i 'The end of the loop
The code above declares an Integer
For loop assigns every value between 1 and 10 to
i and then executes
Debug.Print i - i.e. the code prints the numbers 1 through 10 to the immediate window. Note that the loop variable is incremented by the
Next statement, that is after the enclosed code executes as opposed to before it executes.
By default, the counter will be incremented by 1 each time the loop executes. However, a
Step can be specified to change the amount of the increment as either a literal or the return value of a function. If the starting value, ending value, or
Step value is a floating point number, it will be rounded to the nearest integer value.
Step can be either a positive or negative value.
Dim i As Integer For i = 1 To 10 Step 2 Debug.Print i 'Prints 1, 3, 5, 7, and 9 Next
In general a
For loop would be used in situations where it is known before the loop starts how many times to execute the enclosed code (otherwise a
While loop may be more appropriate). This is because the exit condition is fixed after the first entry into loop, as this code demonstrates:
Private Iterations As Long 'Module scope Public Sub Example() Dim i As Long Iterations = 10 For i = 1 To Iterations Debug.Print Iterations 'Prints 10 through 1, descending. Iterations = Iterations - 1 Next End Sub
For loop can be exited early with the
Exit For statement:
Dim i As Integer For i = 1 To 10 If i > 5 Then Exit For End If Debug.Print i 'Prints 1, 2, 3, 4, 5 before loop exits early. Next
# Select Case
Select Case can be used when many different conditions are possible. The conditions are checked from top to bottom and only the first case that match will be executed.
Sub TestCase() Dim MyVar As String Select Case MyVar 'We Select the Variable MyVar to Work with Case "Hello" 'Now we simply check the cases we want to check MsgBox "This Case" Case "World" MsgBox "Important" Case "How" MsgBox "Stuff" Case "Are" MsgBox "I'm running out of ideas" Case "You?", "Today" 'You can separate several conditions with a comma MsgBox "Uuuhm..." 'if any is matched it will go into the case Case Else 'If none of the other cases is hit MsgBox "All of the other cases failed" End Select Dim i As Integer Select Case i Case Is > 2 '"Is" can be used instead of the variable in conditions. MsgBox "i is greater than 2" 'Case 2 < Is '"Is" can only be used at the beginning of the condition. 'Case Else is optional End Select End Sub
The logic of the
Select Case block can be inverted to support testing of different variables too, in this kind of scenario we can also use logical operators:
Dim x As Integer Dim y As Integer x = 2 y = 5 Select Case True Case x > 3 MsgBox "x is greater than 3" Case y < 2 MsgBox "y is less than 2" Case x = 1 MsgBox "x is equal to 1" Case x = 2 Xor y = 3 MsgBox "Go read about ""Xor""" Case Not y = 5 MsgBox "y is not 5" Case x = 3 Or x = 10 MsgBox "x = 3 or 10" Case y < 10 And x < 10 MsgBox "x and y are less than 10" Case Else MsgBox "No match found" End Select
Case statements can also use arithmetic operators. Where an arithmetic operator is being used against the
Select Case value it should be preceded with the
Dim x As Integer x = 5 Select Case x Case 1 MsgBox "x equals 1" Case 2, 3, 4 MsgBox "x is 2, 3 or 4" Case 7 To 10 MsgBox "x is between 7 and 10 (inclusive)" Case Is < 2 MsgBox "x is less than one" Case Is >= 7 MsgBox "x is greater than or equal to 7" Case Else MsgBox "no match found" End Select
# For Each loop
For Each loop construct is ideal for iterating all elements of a collection.
Public Sub IterateCollection(ByVal items As Collection) 'For Each iterator must always be variant Dim element As Variant For Each element In items 'assumes element can be converted to a string Debug.Print element Next End Sub
For Each when iterating object collections:
Dim sheet As Worksheet For Each sheet In ActiveWorkbook.Worksheets Debug.Print sheet.Name Next
For Each when iterating arrays; a
For loop will offer significantly better performance with arrays. Conversely, a
For Each loop will offer better performance when iterating a
For Each [item] In [collection] [statements] Next [item]
Next keyword may optionally be followed by the iterator variable; this can help clarify nested loops, although there are better ways to clarify nested code, such as extracting the inner loop into its own procedure.
Dim book As Workbook For Each book In Application.Workbooks Debug.Print book.FullName Dim sheet As Worksheet For Each sheet In ActiveWorkbook.Worksheets Debug.Print sheet.Name Next sheet Next book
# Do loop
Public Sub DoLoop() Dim entry As String entry = "" 'Equivalent to a While loop will ask for strings until "Stop" in given 'Prefer using a While loop instead of this form of Do loop Do While entry <> "Stop" entry = InputBox("Enter a string, Stop to end") Debug.Print entry Loop 'Equivalent to the above loop, but the condition is only checked AFTER the 'first iteration of the loop, so it will execute even at least once even 'if entry is equal to "Stop" before entering the loop (like in this case) Do entry = InputBox("Enter a string, Stop to end") Debug.Print entry Loop While entry <> "Stop" 'Equivalent to writing Do While Not entry="Stop" ' 'Because the Until is at the top of the loop, it will 'not execute because entry is still equal to "Stop" 'when evaluating the condition Do Until entry = "Stop" entry = InputBox("Enter a string, Stop to end") Debug.Print entry Loop 'Equivalent to writing Do ... Loop While Not i >= 100 Do entry = InputBox("Enter a string, Stop to end") Debug.Print entry Loop Until entry = "Stop" End Sub
# While loop
'Will return whether an element is present in the array Public Function IsInArray(values() As String, ByVal whatToFind As String) As Boolean Dim i As Integer i = 0 While i < UBound(values) And values(i) <> whatToFind i = i + 1 Wend IsInArray = values(i) = whatToFind End Function