Computer Programming Concepts and Visual Basic David I. Schneider

194 Computer Programming Concepts and Visual Basic
Run, type IBM into the text box, and click the command button.]
Suppose the array contains 100 corporations and the corporation input in Example 5 is in
the second half of the array. On the first pass, middle would be assigned Int((1 + 100)/2) =
Int(50.5) = 50 and then first would be altered to 50 + 1 = 51. On the second pass, middle would
be assigned Int((51 + 100)/2) = Int(75.5) = 75. If the corporation is not the array element with
subscript 75, then either last would be assigned 74 or first would be assigned 76, depending
on whether the corporation appears before or after the 75th element. Each pass through the
loop halves the range of subscripts containing the corporation until the corporation is located.
In Example 5, the binary search merely reported whether or not an array contained a certain
item. After finding the item, its array subscript was not needed. However, if related data
are stored in parallel arrays (as in Table 6.2), the subscript of the found item can be used to
retrieve the related information in the other arrays. This process, called a table lookup, is
used in the following example.
EXAMPLE 6
Use a binary search procedure to locate the data for a city from Example 3 requested by the user.
SOLUTION:
The following program does not include a sort of the data file CITYSTAT.TXT because the file is already
ordered alphabetically.
Dim city(1 To 10) As String, pop(1 To 10) As Single, income(1 To 10) As Single
Dim natives(1 To 10) As Single, advDeg(1 To 10) As Single
Private Sub cmdDisplayStats_Click()
Dim searchCity As String, result As Integer
‘Search for city in the metropolitan areas table
Call GetCityName(searchCity)
Call FindCity(searchCity, result)
picResult.Cls
If result > 0 Then
Call ShowData(result)
Else
picResult.Print searchCity & “ not in file”
End If
End Sub
Private Sub FindCity(searchCity As String, result As Integer)
Dim first As Integer, middle As Integer, last As Integer
Dim foundFlag As Boolean
‘Binary search table for city name
first = 1
last = 10
foundFlag = False
Do While (first searchCity