# GAMBAS BOOK 3.19.2

08.10.2022
k10:start

## 10.0 Control structures

Every task or problem - as a task with a higher level of requirements - whose solution can be described by algorithms, can in principle be solved with the help of the thinking tool computer. This makes the direct correlation between the algorithm and the computer program obvious, which has already been clearly highlighted in chapters 4.5 and 4.6. For the program design, the algorithms for the most important procedures must be available in a suitable form of description - either as text or in another suitable form (natural language - text, pseudo code, structure diagram or also Nassi-Shneiderman diagram) - whereby the representation form (notation) is adapted to the respective task.

When displaying algorithms, you will notice that each algorithm is composed of a few structure elements. These structures are called control structures because they are used to control and control complex (program) sequences. The following control structures are described in this chapter:

• Linear instruction sequence (sequence)
• Selection (case discrimination or selection)
• Repeat (loop or loop)
• Special control structures

## 10.0.1 Selection - Case discrimination or selection

• One-sided selection IF… THEN… ENDIF
• Two-sided selection 1 IIF (selector, A, B)
• Two-sided selection 2 IF… THEN… ELSE… ENDIF
• Multi-selection 1 IF…. THEN…[ ELSE IF.. .. ELSE IF] … ENDIF
• Multiple selection 2 SELECT CASE… END SELECT
• Multi-selection 3 Choose (…)

## 10.0.2 Repeat - Loop

• FOR… TO … STEP… NEXT
• FOR EACH… IN… NEXT
• REPEAT…. UNTIL
• WHILE… WEND
• BREAK and CONTINUE
• DO… LOOP
• Recursion

## 10.0.3 Special control structures

• RETURN
• STOP
• QUIT
• WITH… END WITH
• GOTO
• ON GOTO
• GOSUB
• ON GOSUB
• Application.BUSY

## 10.0.4 Example

The following section introduces an excerpt from the source code of a real project, in which some of the above control structures (For Each..In..Next, For..To..Step..Next, Select.Case, Recursion, If..Then..Else..Endif) the program flow is controlled and controlled in one procedure:

```Public Sub ParseNode(Node As XmlNode)

Dim xmlNode, xmlAttribute As XmlNode
Dim hFeed As FeedItem
Dim iCount As Integer

FOR EACH xmlNode IN Node.Children
IF xmlNode.Name = "item" THEN
hFeed = New FeedItem(ListContainer.Count + 1, ListContainer)
FOR iCount = 0 TO xmlNode.Children.Max STEP 1
xmlAttribute = xmlNode.Children[iCount]
SELECT CASE xmlAttribute.Name
CASE "title"
hFeed.FeedTitle = xmlAttribute.Value
CASE "description"
hFeed.Description = xmlAttribute.Value
END SELECT ' xmlAttribute.Name
NEXT ' iCount
ELSE
IF xmlNode.Children.Count > 0 THEN ParseNode(xmlNode) ' Recursive call!
ENDIF ' xmlNode.Name = "item" ?
NEXT ' Each xmlNode

End ' ParseNode(...) ```