Computer Programming Concepts and Visual Basic David I. Schneider

196 Computer Programming Concepts and Visual Basic
2. In Example 3, parallel arrays already ordered by one field were sorted by another
field. Usually, parallel arrays are sorted by the field to be searched when
accessing the file. This field is called the key field.
3. Suppose an array of 2000 items is searched sequentially—that is, one item after
another—in order to locate a specific item. The number of comparisons would
vary from 1 to 2000, with an average of 1000. With a binary search, the number
of comparisons would be at most 11 because 211 > 2000.
4. The built-in function UCase converts all the characters in a string to uppercase.
UCase is useful in sorting and searching arrays of strings when the alphabetic
case (upper or lower) is unimportant. For instance, Example 5 includes UCase
in the Select Case comparisons, and so the binary search will locate “Mobil” in
the array even if the user entered “MOBIL”.
5. The Visual Basic function Timer can be used to determine the speed of a sort. Precede
the sort with the statement t = Timer. After the sort has executed, the statement
picOutput.Print Timer – t will display the duration of the sort in seconds.
6.5 TWO-DIMENSIONAL ARRAYS
Each array discussed so far held a single list of items. Such array variables are called singlesubscripted
variables. An array can also hold the contents of a table with several rows and
columns. Such arrays are called two-dimensional arrays or double-subscripted variables.
Two tables follow. Table 6.4 gives the road mileage between certain cities. It has four rows and
four columns. Table 6.5 shows the leading universities in three disciplines. It has three rows
and five columns.
TABLE 6.4
Road Mileage Between Selected U.S. Cities
Chicago Los Angeles New York Philadelphia
Chicago 0 2054 802 738
Los Angeles 2054 0 2786 2706
New York 802 2786 0 100
Philadelphia 738 2706 100 0
TABLE 6.5
University Rankings
1 2 3 4 5
Business U of PA U of IN U of MI UC Berk U of VA
Comp Sci. MIT Cng-Mellon UC Berk Cornell U of IL
Engr/Gen. U of IL U of OK U of MD Cng-Mellon CO Sch. of Mines
Source: A Rating of Undergraduate Programs in American and International Universities, Dr. Jack
Gourman, 1998
Two-dimensional array variables store the contents of tables. They have the same types
of names as other array variables. The only difference is that they have two subscripts, each
with its own range. The range of the first subscript is determined by the number of rows in
the table, and the range of the second subscript is determined by the number of columns. The
statement