Arrays Chapter 8

Overview u General discussion u Variable arrays u Control arrays u Multi-dimensional variable arrays  Two-dimensional  Three-dimensional u Parallel arrays u Dynamic arrays

Arrays u Often a set of objects or variables of the same type are used to hold related data  Prices of food items at a fast food restaurant  Scores on programming assignments u In the GPA calculator, rather than having five textboxes with different names to enter the grades, we might better describe the situation as an array of elements  Many data containers  One name

3 Variable Arrays u A variable like Stuff defines a data object into which a single quantity can be placed u A variable like Product defines a data object into which an array of information can be placed Product Stuff

Declaring Variable Arrays u An array is declared using the following syntax: Dim ArrayName(LowerBound To UpperBound) as VariableType u The LowerBound of the array is the lowest index in the array, while the UpperBound is the highest index in the array

Variable Array – Example (1) u Arrays are useful for when there are many instances of similar data u Instead of ten integer variables holding ten values, a single array can handle all ten intd intcinte intj intf intb inta inti inth intg intArray

Variable Array – Example (2) u Each variable location in an array is called an element u Use Dim statement to define size and type Dim intArray(1 to 10) as Integer ‘creates the structure below u Treat as normal variables u Reference using subscripts: intArray(4) = 114 intArray 114

Variable Array – Example (3) u Arrays allow programmers to write code once, but have it applied to many different data elements u Compare adding all the integers stored in the variables… intd intcinte intj intf intb inta inti inth intg intArray intSum = inta + intb + intc _ + intd + inte + intf + intg _ + inth + inti + inj

Variable Array – Example (4) u Arrays allow programmers to write code once, but have it applied to many different data elements u …to adding all the elements of the array intd intcinte intj intf intb inta inti inth intg intArray For intI = 1 to 10 intSum = intSum + intArray(intI) Next intI

Control Arrays u VB allows the programmer to create arrays of controls on the form  Just as there are variable arrays, there may be arrays of objects, such as command buttons, labels, textboxes or picture boxes  An array of labels might be made with one label for each grade point  An array of textboxes might be made with one textbox for each grade, or credits u Characteristics  Name with subscripted elements .Index property is the subscript (Properties Window)

Control Arrays u Using the same procedure, you can make arrays of labels, or of pictures, or of check boxes, etc. u You can change the GPA calculator program to make arrays of grades, credits and grade points

Creating a Control Array – Example u Create an toolbox object, perhaps a command button, changing its (name) and caption.

Creating a Control Array – Example 1.Copy and paste the object (Ctrl-C)(Ctrl-V) or Edit/Copy then Edit/Paste 2.The message “Do you want to create a control array?” appears. Answer “yes” 3.Type Edit/Paste or (Ctrl-V) several more times to make an array of commands

Creating a Control Array – Example u The Properties Window shows it all. u Note that the 4th command created is shown as “cmdButn(3)”

Creating a Control Array – Example u Arrange the buttons on the form as desired u Double clicking on any one of them opens the code window

Creating a Control Array – Example u The event handler is a bit strange. There is now a “parameter” inside the normally blank parentheses: Private Sub cmdButn_Click(Index As Integer) lblOutput.Caption = "## " & Index & " ##" End Sub

Creating a Control Array – Example u Run the process u Click each button u Observe the effect

Creating Multi-dimensional variable Arrays u Arrays can come in different dimensions u You need to specify the lower and upper bounds for each dimension  Array name; Dimensions; Bounds; Type  An example of a two-dimensional array: Dim strName (1 to 3, 1 to 4) as String

Advanced Variable Arrays u Multi-dimensional arrays u Parallel arrays u Searching arrays u Dynamic Arrays

Creating Multi-dimensional variable Arrays u When accessing/storing elements in the array…  Any integer literal, variable or expression can be used to subscript  Must stay within the bounds  Must have the correct number of subscripts  If storing, must assign the correct type of data u Given: Dim strName (1 to 3, 1 to 4) as String  Is strName (0, 0) = “Jones” valid?  Is strName (2) = “Smith” valid?  Is strName (4, 3) = “Larry” valid?  Is strName(3, 4) = 1402 valid?

Two-dimensional variable Arrays u Two dimensional arrays  require two subscripts  elements are listed (row, column) u Example Dim intSales(1 to 3, 1 to 4) _ as Integer u What is intSales(2, 3)?

Three-dimensional variable Arrays u Three dimensional arrays  require three subscripts (row, column, depth) u Example  Dim intSales (1 to 3, 1 to 4, 1 to 2) as Integer So the number 2134 is found where? the number 4521 is ______ the number 1402 is ______ the number 3425 is ______

Parallel Arrays u Parallel arrays are used to hold related data with different types  Dim strName (1 to 5) as String  Dim intSales (1 to 5) as Integer  So, if we know that Smith is in strName(2), we also know his or her sales is in intSales(2) strName intSales Jones Smith Frank Able Zean

Searching Arrays strTarget = "Q" intFound = 0 For intI = 1 to 10 If strTarget = strArray(intI) Then intFound = intI Exit For End If Next intI strArray A F S V W Q Z X Y L Searching implies looking for a target A simple sequential search looks through the array for the target

Dynamic Arrays u You can re-dimension an array at run-time u Rules for resizing arrays:  Use can empty dimension list: Dim intArray() as Integer  Use ReDim to assign dimensions: ReDim intArray (1 to intN, 1 to 2)  Use ReDim to change Bounds ReDim intArray (1 to (intN + 10), 1 to 3)  Use Preserve keyword to save data in array ReDim Preserve intArray(1 to intN, 1 to 5)