Arrays

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Chapter 7

• Arrays

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Ordered Array

• An array is ordered it its values are in either
  ascending or descending order.
• For string arrays, the ANSI table is used to
  evaluate the less than or equal to condition.

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Ordered Array

• An array is ordered it its values are in either
  ascending or descending order.
• For string arrays, the ANSI table is used to
  evaluate the less than or equal to condition.

4
Processing Arrays

• Searching successive elements of an array is
  called Sequential Search.
• Also called linear search or serial search.
• A Sequential Search examines each element , from
  the first to the last, until the specified value
  is found or the end of the array is reached.

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Example of Sequential Search (finding the quiz
grades greater than 8)

• Dim quiz ( 1 To 15) As Single
• For position 1 TO 15
• If quiz(position) gt 8 THEN
• picOutput.Print quiz (position)
• count count 1
• End If
• Next Position

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Sequential Search

• Useful for short lists.
• Very inefficient for long lists ( example names
  in telephone book).
• Use binary search if the list is sorted.

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Binary Search

• In binary search, an ordered array is repeatedly
  divided in half. The half not containing the
  target value is ignored.
• To use binary search, the data in the array must
  be arranged in ascending or descending order.

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Binary Search

• Private Sub BinarySearch(corp As String, result
  As String
• foundFlag 0 '1 indicates corp
  found
• first 1
• last numFirmsDo While (first lt last) And
  (foundFlag 0) middle Int((first last)
  / 2) Select Case UCase(firm(middle))
  Case corp foundFlag 1 Case
  Is gt corp last middle - 1
  Case Is lt corp first middle 1
  End Select
• Loop
• End Sub

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Binary Search

• If foundFlag 1 Then
• result "found
• Else
• result "not found
• End If

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Merging

• A common practice involving arrays is merging two
  sorted arrays.

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The method for merging two sorted arrays

• 1.Compare the two first elements of the first and
  second arrays.
• A. If one name alphabetically precedes the other,
  copy it onto the third list and cross it off the
  original array.
• B. If the names are the same, copy the name onto
  the third list and cross out the name from both
  arrays.
• 2. Repeat Step 1 with the new name in the array
  until you reach the end of either array.
• 3. Copy the names from the remaining array onto
  the third array.

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Passing an Array

• An array can be passed to another procedure by
  reference.

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Example of Passing an array

• Private Sub cmddisplay_Click()
• ' Pass array to subprogram and function
• Dim score(1 To 5) As Integer
• Call FillArray(score( ) )
• picAverage.Cls
• picAverage.Print Average is" Sum(score( ) )
  / 5
• End Sub

Passing array score
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Array Score is passed to a Subprogram

• Private Sub FillArray(s( ) As Integer)
• ' Fill array with scores
• s(1) 85
• s(2) 92
• s(3) 75
• s(4) 68
• s(5) 84
• End Sub

This array is pointing to the same location as
array score
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Array Score is passed to a Function

• Private Function Sum(s ( ) As Integer) As Integer
• Dim total As Integer, index As Integer
• ' Add up scores
• total 0
• For index 1 To 5
• total total s(index)
• Next index
• Sum total
• End Function

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Homework

• P. 341 1-19 Odd Problems