Computer Programming Concepts and Visual Basic David I. Schneider

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[Run, and then click on the command button. The following is displayed in the picture box.]
Ringo 1940
Barbra 1942
Sylvester 1946
■ MERGING SEQUENTIAL FILES
In Section 6.2, we considered an algorithm for merging two arrays. This same algorithm can
be applied to merging two ordered files.
Suppose you have two ordered files (possibly with certain items appearing in both files),
and you want to merge them into a third ordered file (without duplications). The technique
for creating the third file is as follows.
1. Open the two ordered files For Input and open a third file For Output.
2. Try to get an item of data from each file.
3. Repeat steps (a) and (b) below until an item of data is not available in one of
the files.
(a) If one item precedes the other, write it into the third file and try to get another
item of data from its file.
(b) If the two items are identical, write one into the third file and try to get
another item of data from each of the two ordered files.
4. At this point, an item of data has most likely been retrieved from one of the files
and not yet written to the third file. In this case, write that item and all remaining
items in that file to the third file.
5. Close the three files.
EXAMPLE 2
The following program merges two ordered files of numbers into a third file.
Object Property Setting
frmMerge Caption Merge Two Files
lblNameFirst Caption Name of first file:
txtNameFirst Text (blank)
lblNameSecond Caption Name of second file:
txtNameSecond Text (blank)
lblNameMerged Caption Name for merged file:
txtNameMerged Text (blank)
cmdProceed Caption Proceed to Merge
picProgress
Private Sub cmdProceed_Click()
Dim file1 As String, file2 As String, file3 As String
Dim have1data As Boolean, have2data As Boolean
Dim num1 As Single, num2 As Single
Dim recCount As Integer ‘Number of records in merged file
‘Merge two ordered files
picProgress.Cls
file1 = txtNameFirst.Text
file2 = txtNameSecond.Text
file3 = txtNameMerged.Text
Open file1 For Input As #1
Using Sequential Files 225