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Introduction to Computer Programming IT-104 Unit Six – Arrays

Objectives. Introduction. Loop Types. Determinate. Indeterminate. Event. While-Wend. Do-While. Do-Until. For-Next. Exit. Introduction to Computer Programming IT-104 Unit Six – Arrays. Objectives. Understand the use of control, list, and table arrays in Visual Basic

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Introduction to Computer Programming IT-104 Unit Six – Arrays

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  1. Objectives Introduction Loop Types Determinate Indeterminate Event While-Wend Do-While Do-Until For-Next Exit • Introduction to Computer Programming IT-104 Unit Six – Arrays Intro to Comp. Programming - IT 104

  2. Objectives • Understand the use of control, list, and table arrays in Visual Basic • Use control arrays to work with groups of controls using a single name. • Describe the difference between arrays and combo boxes, list boxes, and similar controls. • Declare the maximum number of elements or rows and columns for an array. Intro to Comp. Programming - IT 104

  3. Objectives • Understand the errors that can occur from exceeding the declared upper limits on index values. • Input data into an array from the keyboard or files using loops. • Manipulate array data to find the sum and average of array values, the largest or smallest value in an array, or to find a particular value. • Work with multiple arrays to match values in one array to those in the other. Intro to Comp. Programming - IT 104

  4. Objectives • Output the result of array processing to a control, the printer, or the Immediate window. • Use Step operations to step though an array operation to find and correct an error. Intro to Comp. Programming - IT 104

  5. Introduction Home Arrays are an important part of computer programming. An Array is a special type of variable structure implemented in virtually every computer language. Without the array and the loop collectively, programming a computer would be a daunting task indeed. Intro to Comp. Programming - IT 104

  6. Using Control Arrays • A control array is group of the same type control which isassigned a single name****. • The individual controls are identified by the control array name and an index value starting with 0.**** • The Case decision structure can be useful in working with a control array. • To create a control array, just enter the same Intro to Comp. Programming - IT 104

  7. Using Control Arrays Home name for more than one control and replay “yes” to the query. • Alternatively, simply copy an existing control and paste it to your existing form, and then answer ‘Yes’ to the ‘Confirm Control Array’ dialog box. • The order in which the controls are entered determines the index values for the controls in the control array. Intro to Comp. Programming - IT 104

  8. Check Boxes Vs. Option Buttons Home • Check box is used to make multiple selections from a list • Prefix is chk • Option button is used to make one selection from a list. • Often referred to as radio buttons • Prefix is opt Intro to Comp. Programming - IT 104

  9. Frame Control Home • Option buttons must be within a frame control which acts as a container . • Frames have a prefix of fra. • Recommendation is to add frame first and add the option button by drawing it in, not double clicking. Intro to Comp. Programming - IT 104

  10. Frame Control • All option buttons will have the same name but a different Index, such as optDemo(0), optDemo(1), optDemo(2). • If the frame is moved, option buttons will move withit. Intro to Comp. Programming - IT 104

  11. Option Button Array Home • Double click any option button to open the code window and it will have event similar to this : Private Sub optDemo_Click(Index as Integer) • The Index value is being passed to the event procedure, in other words, the index of the option button that was clicked is now known to the event procedure. • The Index value is used is Select Case statements. Intro to Comp. Programming - IT 104

  12. VB Code for Option Buttons Private Sub optDemo_Click(Index As Integer) Select CaseIndex Case 0 MsgBox "Button One selected" Case 1 MsgBox "Button Two selected" Case 2 MsgBox "Button Three selected" End Select End Sub Intro to Comp. Programming - IT 104

  13. Check Box Control Array • All check boxes will have the same name but a different Value, such as chkSelect(0).Value, chkSelect(1).Value, chkSelect(2).value • The Value will either be True or False. It is True if the check box is selected and False if not selected • To determine if it is False use the Not operator • Code on Next slide is used to check if a value is True or False Intro to Comp. Programming - IT 104

  14. VB Code for Check Box Control Array Private Sub cmdSelect_Click() If chkSelect(0).Value And Not chkSelect(1).Value Then MsgBox "Box One selected" ElseIf Not chkSelect(0).Value And chkSelect(1).Value Then MsgBox "Box Two selected" ElseIf chkSelect(0).Value And chkSelect(1).Value Then MsgBox "Boxes One and Two selected" Else MsgBox "No boxes selected" End If End Sub Intro to Comp. Programming - IT 104

  15. VB Code Select Prices Using Option Buttons (Pos demo) Private Sub OptTypes_Click(Index As Integer) Dim curItemPrice As Currency Select Case Index Case 0 ’Perishables curItemPrice = 3.99 Case 1 ’Staples curItemPrice = 1.99 Case 2 ’Hardware curItemPrice = 5.99 Case 3 ‘Cleaning supplies curItemPrice = 2.99 End Select txtItemPrice.text = Format(curItemPrice, "currency") End Sub Intro to Comp. Programming - IT 104

  16. VB Code to Clear the OptTypes Option Buttons Home Private Sub cmdClear_Click() For Counter = 0 to 2 ’Clear option buttons OptTypes(Counter).Value = False Next End Sub Intro to Comp. Programming - IT 104

  17. Using List Arrays • Arrays are lists or tables of data which have single name. They provide a way of working with long lists in memory versus working with short lists in a list or combo box. • Arrays can only store one type of data. • Individual array elements are identified by the array name and one or more subscripts or index values. For instance: curPrices(0), curPrices(1), curPrices(2) • The index must be an integer constant, variable or Intro to Comp. Programming - IT 104

  18. Using List Arrays expression. • To be used in Visual Basic, an arraymust be declared just like any other variable. • Arrays can be fixed size or dynamic size (we use only fixed arrays.) • Fixed size-array- specific amount of memory set aside for it. • Dynamic array - no fixed amount of memory is reserved. Intro to Comp. Programming - IT 104

  19. Using List Arrays • Form of array declaration : Dim ArrayName (max index value) as variable type Dim curPrices(9) as Currency • Above statement allows for 10 values to be stored (0-9) • The declaration statement defines the upper limit but by default the lower limit on an array index is zero but this can be changed to one or any other value. • It is not possible to exceed the upper limit or go below the lower limit on the array index values . Will receive a “Subscript out of range” error Intro to Comp. Programming - IT 104

  20. Using List Arrays Home • If a lower bound other than zero is desired, the programmer can implement his own numbering scheme as in the following: • Dim sngRate(100 to 199) as Single • This statement allocates 100 elements, but the lower bound is now 100 instead of 0. This gives the programmer the flexibility of matching existing numbering schemes that may exist within files he has been given to process. Intro to Comp. Programming - IT 104

  21. Entering Event Driven Array Data • Most of the time you want to input multiple values into an array. • Arrays can be input with any of the three types of loops discussed earlier--event driven, for-next, or while/until loops. • If input is from a keyboard and you don’t know the values to be input, an event driven loop is most appropriate. Similar to loops in Chapter 5 except values are entered directly in an array versus being added to a list box. Values don’t need to be summed Intro to Comp. Programming - IT 104

  22. Entering Event Driven Array Data immediately. • Index for the array corresponds to the value of the counting variable for each value that is input. • With an event driven loop, each click of a button increments a counter and inputs the corresponding array element. Intro to Comp. Programming - IT 104

  23. Input Using For-Next Loops • With a For-Next loop, you must input the number of arrays elements. The array values must be input with an Inputbox with the For-Next counter variable matching the array index Private Sub Input_Click() Dim intCounter As Integer intNumPrices = CInt(InputBox("How many prices?")) For intCounter = 0 To intNumPrices - 1 curPrices(Counter) = CCur(InputBox("Next price:")) Next End Sub Intro to Comp. Programming - IT 104

  24. Processing Arrays • Typical array operations include summing and averaging the array values and finding the largest or smallest value in the array. • Working with arrays usually involves a For-Next loop. • Summing Prices array elements involves using a statement of the form: Sum = Sum + Prices(Counter) • Averaging Prices array elements involves dividing the Sum by the number of elements Intro to Comp. Programming - IT 104

  25. Processing Arrays • Finding the largest or smallest value involves multiple comparisons of array elements. • To find the maximum Price, you must compare each array value to the current highest price; if it is higher, it becomes the highest price. Do this using For-Next loop and If-then Intro to Comp. Programming - IT 104

  26. VB Code to Compute the Sum and Average in Array Home Private Sub CmdSumAverage_Click() Dim curSum as Currency’Sum variable Dim intCounter as Integer’counter variable Dim curAverage as Currency’Average variable curSum = 0 ’Set sum to 0 For intCounter = 0 to intNumPrices - 1 curSum = curSum + curPrices(intCounter) ’add prices Next If intNumPrices >0 Then’check to see if >0 curAverage = curSum/intNumPrices ’true average prices Else’if false MsgBox "No values to average!” ’display Msgbox Exit Sub End If txtSum.Text=Format(curSum, “currency”) txtAverage.Text = Format (curAverage, “currency” End Sub Intro to Comp. Programming - IT 104

  27. Pseudocode to Find Maximum Value Begin procedure to find largest value Set largest value to first item in list Repeat beginning with second item to last item If item in list > largest value then Largest value = item in list End decision End repeat Display largest value End procedure Intro to Comp. Programming - IT 104

  28. VB Code to Find Maximum Value in List Private Sub cmdFindMax_Click() ’Declare variables and set largest value to first item in the array Dim intCounter As Integer, curLargest As Currency curLargest = curPrices(0) For intCounter = 1 To intNumPrices - 1 If curPrices(intCounter) >curLargest Then’if item >largest # curLargest = curPrices(intCounter) ’ replace it if it is larger End If Next ’Display largest number as currency txtMaxPrice.Text = Format(curLargest, "currency") End Sub Intro to Comp. Programming - IT 104

  29. Code to Find Minimum Value in List Private Sub cmdFindMin_Click() ’Declare variables and set smallest value to first item in the array Dim intCounter As Integer, curSmallest As Currency curSmallest = Prices(0) For intCounter = 1 To intNumPrices - 1 If curPrices(intCounter) < curSmallest Then’if item > smallest # curSmallest = Prices(Counter) ’ replace if it is smaller End If Next ’Display smallest number as currency txtMaxPrice.Text = Format(curSmallest, "currency") End Sub Intro to Comp. Programming - IT 104

  30. Find the Largest/Smallest String Value in a List • Collating Sequence - order in which characters are displayed • Digits come before alphabetic characters. • Upper case A is smaller than uppercase B because it comes first in alphabetical ordering • Lower case letters come after upper case letters • Chr() function converts Integer values of the For-Next variable into the corresponding characters • To reverse operation use the ASC() function with the character as the argument Intro to Comp. Programming - IT 104

  31. VB Code for Displayingthe Collating Sequence Private Sub Form_Load() Dim intCounter As Integer For intCounter = 0 To 255 Debug.Print Chr(intCounter); Next End Sub Intro to Comp. Programming - IT 104

  32. Finding Items and Working with Multiple Lists • The goal of the project is to find a specified part ID and display the part identifier and the price of the part • To input both the part identifiers and a price a second array, PartID needs to be declared as a string in the Form General declaration section • Dim strPartId(25) as String • The Input Statement in the Form-Load event must be modified • Input #5, strPartID(intNumPrices), curPrices(intNumPrices) • For a given part, the index values or the strPartId, and the curPrices arrays are the same. The index acts as a link between them. Intro to Comp. Programming - IT 104

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