Computer Programming Concepts and Visual Basic David I. Schneider

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lblColLab() Caption A
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txtCell() Text (blank)
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■ CODING THE PROGRAM
A Case Study: Calculating with a Spreadsheet 203
The top row of Figure 6-12 shows the different events to which the program must respond.
Table 6.8 identifies the corresponding event procedures and the general procedures they call.
Let’s examine each event procedure.
1. Form_Load assigns the number of rows (16) and columns (6) in our spreadsheet
to the form-level variables maxRow and maxCol. Form_Load then calls
three general procedures to create and initialize the spreadsheet.
The procedure CreateSpreadsheet loads each element of the txtCell( ) control
array in order from left to right, top to bottom. Cell 1, which is to be the first
cell in the first row, is not loaded because it was created at design time. The Top
property of a new cell is set so that the top edge of the new cell overlaps the
bottom edge of the previous cell in the column. The Top property of the first
cell in a column is not modified, and so the value of the Top property is the
same as cell 1. Similarly, the Left property of a new cell is set so that the left
edge of the new cell overlaps the right edge of the previous cell in the row. The
Left property of the first cell in a row is not modified, and so the value of the
Left property is the same as cell 1. CreateSpreadsheet also loads the additional
row and column label elements and assigns an appropriate caption. Create-
Spreadsheet’s final task is to set the Height and Width properties of frm-
SpreadSheet to accommodate all the objects that have been loaded. The
numbers 500 and 200, which appear in these statements, were obtained by trial
and error and are necessary to account for the space used by the form caption
and borders.
The procedure SetStructure assigns heading values to various cells of the
spreadsheet in accordance with the specific application we were asked to program.
The user will not be able to alter the value in these cells, because the rules
for which cells are to be totaled, and where these totals are to be placed are
“hard wired” into the program and cannot be changed by the user. SetStructure
also assigns values to a set of form-level variables so that other procedures in
the program can be coded using meaningful names rather than possibly obscure
numbers. Besides Form_Load, SetStructure is also called by the
cmdNew_Click event procedure.
The procedure SetDefaults assigns the income and expense category headings
shown in Figure 6-9 to the appropriate cells. The user may change these headings
at any time, and must supply them if the “New” command is issued.
2. txtCell_GotFocus checks to see if the cell that has received the focus may,
according to the rules of this application, be edited by the user. The row and column
numbers for the cell are computed from the cell’s index. If the cell that has
received the focus is in a column after stopCol, the last editable column, then the
column to be edited is changed to startCol, the first editable column, and the row
to be edited is advanced by one. If the row to be edited does not contain any
editable cells, then the row to be edited is advanced to the next row containing
editable cells. (When the focus goes past the last row of editable cells, the next
editable row is the first editable row, that is, incStartRow.) Finally, focus is set to
the adjusted row and column, but only if an adjustment has been made. If the test
Indx(row,col)Index were not made and focus were reset to a cell that already