Chapter 7: Working with Arrays

1
Chapter 7 Working with Arrays

• Visual Basic .NET Programming
• From Problem Analysis to Program Design

2
Objectives

• Define one-dimensional arrays
• Create String arrays
• Declare multi-dimensional arrays
• Search an array

3
Arrays

• Array is a collection of elements with each
  element behaves as a variable does

4
Arrays

• To declare array syntax
• Dim arrayName (index of last element) As DataType
• Example

5
Arrays (continued)

• Arrays could be multi-dimensional
• An array is managed as an object (array class)
• Arrays are static

6
Using a Loop to Iterate an Array

• Use loop to process array elements
• Repeat program code for each element

Dim examScores(4) As Integer, sum, average As
Double Dim index As Integer ' loop to enter and
sum the exam scores For index 0 To
examScores.Length 1 Console.WriteLine("Enter
an Exam Score ") examScores(index)
Convert.ToInt32(Console.ReadLine()) sum
examScores(index) Next average sum /
examScores.Length Console.WriteLine("The average
is " Math.Round(average, 1))
7
Array Methods

• Sort Array.Sort( examScores )
• Reverse Array.Reverse( examScores )

Dim examscores() As Integer 85, 90, 94, 89,
91 Dim index As Integer Console.writeLine(Unsort
ed array) For index 0 To examScores.Length
1 Console.Write(examScores(index) ,
) Next Array.Sort(examScores) Console.WriteLine()
Console.WriteLine(Sorted array) For index 0
To examScores.Length 1 Console.Write(examScores
(index) , ) Next
8
The String Array

• Each element in a string array is a string
• To extracts substrings separated by a character
  value (empty space). Letter c indicates the
  data type
• Dim stringArray() As String stringValue.Split(
  c)

Dim stringValue As String Hello world Wide
web, i As Integer Dim stringArray() As String
stringValue.Split ( c) For i 0 To
stringArray.Length 1 Console.writeLine(
stringArray(i) ) Next Console.writeLine(
stringArray.Length elements
) Console.writeLine( length of Web is
stringArray(3).Length ) Console.writeLine(
stringArray(0).ToUpper() )
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10
Multi-Dimensional Arrays

• Two-dimensional array is like a table with rows
  and columns
• Dim testScoreTable(4, 1) As Integer
• Accessing elements in two-dimensional array
  example

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Example Compute the First Exam Average

• Dim testScoreTable(,) As Integer _
• 85, 88, 90, 85, 94, 60, 89, 95, 91,
  100
• ' compute Exam 1 average using a loop
• Dim sum As Double, row As Integer
• For row 0 To 4
• sum testScoreTable(row, 0)
• Next
• Console.WriteLine( Exam 1 average is sum / 5
  )

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Searching an Array

• Search array to see if it contains specific value
• Use loop to compare each value to target

Dim stringValue As String Hello orld Wide
web Dim stringArray() As String
stringValue.Split( c) Dim searchValue As String
Web, found As Boolean False Do While i lt
stringArray.Length And Not found If
stringArray(i).Equals(searchValue) Then found
True Else i 1 End If Loop
14
Example Employee Payroll

• Problem to be solved to input employees taxable
  wages and marital status, and to compute and
  display amount of federal tax (in currency
  format) to be withheld
• Use arrays to hold tax tables
• Input
• Taxable wages
• Marital status
• Output
• Amount of federal tax to be withheld

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Example Employee Payroll

• Imports System.Collections.ArrayList
• ...
• single employee table
• Dim singleTaxTable(,) As Double
• 51, 0, 0, 0, 187, 0, 0.1, 51, 592, 13.6,
  0.15, 187, _
• 1317, 74.35, 0.25, 592, 2860, 255.6, 0.28,
  1317, _
• 6177, 687.64, 0.33, 2860, 99999, 1782.25,
  0.35, 6177
• ' married employee table
• Dim marriedTaxTable(,) As Double
• 154, 0, 0, 0, 429, 0, 0.1, 154, 1245,
  27.5, 0.15, 429, _
• 2270, 149.9, 0.25,
  1245, 3568, 406.15, 0.28, 2270, _
• 6271, 769.59, 0.33,
  3568, 99999, 1661.58, 0.35, 6271
• Dim taxTable(,) As Double,
  marriedOrSingle As Char
• Dim msIndex, rowIndex As Integer, wages,
  fedWithholding As Double
• Dim found As Boolean

16
Example Employee Payroll

• ' use 99999 as sentinal value to terminate
• Console.Write("Enter wage amount (99999
  to stop)")
• wages Convert.ToDouble(Console.ReadLine(
  ))
• ' begin the loop for each employee
• Do Until wages 99999
• Console.Write("Enter M for married, S
  for single")
• marriedOrSingle Convert.ToChar(Cons
  ole.ReadLine())
• ' assign taxTable reference to
  appropriate table
• If marriedOrSingle "M" Then
• taxTable marriedTaxTable
• Else
• taxTable singleTaxTable
• End If
• rowIndex 0
• found False

17
Example Employee Payroll

• ' loop to find the appropriate row for the
  wages
• Do While rowIndex lt 6 And found
  False
• If wages lt
  taxTable(rowIndex, 0) Then
• ' compute the withholding
  amount
• fedWithholding
  taxTable(rowIndex, 1) _
• taxTable(rowIndex, 2) (wages -
  taxTable(rowIndex, 3))
• found True ' stop the loop
• Else
• rowIndex 1
• End If
• Loop
• Console.WriteLine("Federal
  Withholding " fedWithholding.ToString("C"))
• ' input wage amount for next
  employee
• Console.Write("Enter wage amount
  (99999 to stop)")
• wages Convert.ToDouble(Console.Read
  Line())
• Loop