Computer Programming Concepts and Visual Basic David I. Schneider

■ THE DESIGN OF THE PROGRAM
Figure 6-9 contains an example of a spreadsheet used to analyze a student’s financial projections
for the four quarters of a year. Column F holds the sum of the entries in columns B
through E, rows 6 and 14 hold sums of the entries in rows 3 through 5 and 9 through 13, respectively,
and row 16 holds the differences of the entries in rows 6 and 14. Because the total
balance is negative, some of the amounts in the spreadsheet must be changed and the totals and
balances recalculated.
A B C D E F
1 Fall Winter Spring Summer Total
2 Income
3 Job 1000 1300 1000 2000 5300
4 Parents 200 200 200 0 600
5 Scholarship 150 150 150 0 450
6 Total 1350 1650 1350 2000 6350
7
8 Expenses
9 Tuition 400 0 400 0 800
10 Food 650 650 650 650 2600
11 Rent 600 600 600 400 2200
12 Books 110 0 120 0 230
13 Misc 230 210 300 120 860
14 Total 1990 1460 2070 1170 6690
15
16 Balance –640 190 –720 830 –340
FIGURE 6-9 Spreadsheet for Student’s Financial Projections
The 96 locations in the spreadsheet that hold information are called cells. Each cell is
identified by its row number and column letter. For instance, cell 14, C contains the amount
1460. For programming purposes, each column is identified by a number, starting with 1 for
the leftmost column. Thus cell 14, C will be cell 14, 3 in our program.
This case study develops a program to produce a spreadsheet with the five columns of
numbers shown in Figure 6-11, three user-specified categories of income, and five user-specified
categories of expenses. The following tasks are to be selected by command buttons:
1. Start a new spreadsheet. All current category names and values are erased and
the cursor is placed in the text box of the first income category.
2. Quit.
Three additional tasks need to be performed as the result of other events:
1. Create the spreadsheet when the form is loaded.
2. Limit the user to editing category names and quarterly values.
3. Display totals after a change is made in the spreadsheet.
■ THE USER INTERFACE
A Case Study: Calculating with a Spreadsheet 201
Each cell in the spreadsheet will be an element of a text box control array. A control array of
labels is needed for the numeric labels to the left of each row and another control array of labels
for the alphabetic labels at the top of each column. Finally, two command buttons are required.
The task of controlling which cells the user can edit will be handled by a GotFocus
event. The task of updating the totals will be handled by a LostFocus event. Figure 6-10 shows
one possible form design with all control elements loaded. For this application of a spreadsheet,
the headings that have been assigned to cells in rows 1, 2, 6, 8, 14, and 16 are fixed; the user
will not be allowed to edit them. The other entries in column A, the category names, may be
edited by the user, but we have provided the set from Figure 6-9 as the default.