Computer Programming Concepts and Visual Basic David I. Schneider

14. Variable names should describe the role of the variable. Also, some programmers
use a prefix, such as sng or str, to identify the type of a variable. For example,
they would use names like sngInterestRate and strFirstName.
2.5 INPUT AND OUTPUT
So far we have relied on assignment statements to assign values to variables. Data also can be
stored in files and accessed through Input # statements, or data can be supplied by the user in
a text box or input box. The Print method, with a little help from commas and the Tab function,
can spread out and align the display of data in a picture box or on a printer. Message
boxes grab the user’s attention and display temporary messages. Comment statements allow
the programmer to document all aspects of a program, including a description of the input
used and the output to be produced.
■ READING DATA FROM FILES
In Section 1, we saw how to create data files with Windows’ Notepad. (As a rule of thumb, and
simply as a matter of style, we enclose each string in quotation marks.) A file can have either
one item per line or many items (separated by commas) can be listed on the same line. Usually,
related items are grouped together on a line. For instance, if a file consisted of payroll information,
each line would contain the name of a person, that person’s hourly wage, and the number
of hours that person worked during the week, as shown in Figure 2-24.
FIGURE 2-24 Contents of STAFF.TXT
“Mike Jones”, 7.35, 35
“John Smith”, 6.75, 33
The items of data will be assigned to variables one at a time in the order they appear in
the file. That is, “Mike Jones” will be the first value assigned to a variable. After all the items
from the first line have been assigned to variables, subsequent requests for values will be
read from the next line.
Data stored in a file can be read in order (that is, sequentially) and assigned to variables
with the following steps.
1. Choose a number from 1 to 255 to be the reference number for the file.
2. Execute the statement
Open “filespec” For Input As #n
where n is the reference number. This procedure is referred to as Opening a file
for input. It establishes a communications link between the computer and the
disk drive for reading data from the disk. Data then can be input from the specified
file and assigned to variables in the program.
3. Read items of data in order, one at a time, from the file with Input # statements.
The statement
Input #n, var
causes the program to look in the file for the next available item of data and
assign it to the variable var. In the file, individual items are separated by commas
or line breaks. The variable in the Input # statement should be the same
type (that is, string versus numeric) as the data to be assigned to it from the file.
4. After the desired items have been read from the file, close the file with the
statement
Close #n
Input and Output 49