Arrays

Overview u General Discussion  Uses  Structure  Declaration u Searching u Control Arrays

Arrays u From time to time an object (a variable, a picture, a label or a command) does not serve as well as a set of objects of a similar kind addressed with a common name. u For example, in the grade point calculator, rather than having hamburgers, fries and drinks each with its own price and quantity measures, we might better describe the situation as an array of elements

3 Data 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

Arrays 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

Arrays u Each variable location in an array is called an element u Use Dim statement to create, define dimension and type Dim intArray(1 to 10) as Integer creates the structure below u Treat as normal variables; Reference using subscripts: intArray(4) = “114” intArray 114

Arrays 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

Arrays 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

Arrays u Arrays come in different dimensions. 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)?

Arrays u Three dimensional arrays  require three subscripts 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 Dim strName (1 to 5) as String u Dim intSales (1 to 5) as Integer u 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

Creating Arrays u Dim statement  Array name; Dimensions; Bounds; Type Dim strName (1 to 3, 1 to 4) as String u Using  Any integer literal or variable can be used to subscript  Must stay within the bounds  Must have the correct number of subscripts  Must assign the correct type of data  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?

Searching Arrays strTarget = “Q” intFound = 0 For intI = 1 to 10 If strTarget = strArray(intI) Then intFound = intI Exit For End If Next 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 VB allows a programming to re-dimension arrays during the run of the program. u Rules for Dynamic Arrays  Use empty dimension list: 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) Preserve only allows changes in the last dimension

Control Arrays u VB allows the programmer to create arrays of controls on the form  Just as there are data arrays, there may be arrays of objects, such as command buttons, labels or picture boxes  An array of labels might be made with one label for each product, or for each price  An array of command might be made to handle adding products u Characteristics  Name with subscripted elements .Index property is the subscript

Control Arrays u Create an toolbox object, perhaps a command button, changing its (name) and caption.

Control Arrays 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

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

Control Arrays u Arrange the buttons on the form as desired u Double clicking on any one of them opens the code window

Control Arrays 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

Control Arrays u Run the process u Click each button u Observe the effect

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 products, commands, product counts, and total costs

Summary u Arrays are sets of variables know as elements u These elements operate just like simple variables u Arrays are created with a DIM statement that defines; boundaries, dimensions and type u When referencing elements in an array, you must have the correct number of subscripts and their values must be within the bounds of the dimensions u The operation of looking through an array for a “target” is called searching