LAB 7.2 - Simple File I/O
CIS241
Goals:
w Create a data file with a text editor
w Read a specified amount of data from a file
w Read data from a file using a flag as end of file marker
w Read data from a file using EOF
w Read data from a file character by character
w Write data to a file
__1. Begin a new VB project, renaming & saving as previously specified.
__2. Open
Notepad and create a text filew Type in 10 integers, each on a separate line, followed by -1
w Save the file as numbers.txt (be sure to save this file in the same
folder as your VB project)
__3. Write a count controlled loop to process the values in that file
w Get some information from online Help
v Click on Help on the menu bar, choose Index, and type Print.
v Double click on Print # statement
v Click on Edit in the MSDN menu bar, choose Find in this Topic
and type in read. What do you think the VB keyword is for
reading from a file?
v Find information on that VB keyword. When you do click on
Example and study the example shown.
w Place a command button on the form and write code to:
v Open the file for input (use the code below)
Open App.Path & "\numbers.txt" For Input As #1
v Read 10 values from the file, summing them. For reading use
a statement similar to the one below
Input #1, val
v Print the sum of those numbers as the caption of a label
v Close the input file.
__4. Add processing to the loop
w Add code to the above to find the minimum and maximum values
read from the input file.
v Declare two variables, say max and min
v Initialize max to the smallest possible integer value
v Initialize min to the largest possible integer value
v Inside the loop add this line of code for min
&#If val < min Then min = val
v And add a similar line for max
w Use labels to output those values to the screen.
__5. Write a flag controlled loop to process the values in that file
w Place a second command button on the form
w Write code for processing using a While-Wend loop
v Place a read statement immediately before the loop
{This is known as a priming read}
v Copy and paste as much of the code from the For loop as
seems appropriate. Make any necessary adjustments.
v Place a second read statement at the very end of the loop body,
immediately before the
Wend.v Let the test condition of the loop be that the value read is -1.
w Test your program. Does this loop give the same results?
__6. Write an EOF controlled loop to process the values in that file
w Check out EOF in online Help
v Type eof into the Help Index
v Double click on EOF Function
v Look over the entry and study the example
w Place a third command button on the form
w Write code for processing controlled by EOF
v Copy and paste the code from the while loop
v Change the test to read as below:
While Not EOF(1)
w Test your program. Does this loop give the same results as before?
__7. Write a loop to process the file a character at a time
w Place a fourth command button on the form & use the code below
Dim chval As String * 1
Open App.Path & "\numbers.txt" For Input As #1
Open App.Path & "\record.txt" For Output As #2
chval = Input(1, #1)
While Not EOF(1)
Print #2, chval, Asc(chval)
chval = Input(1, #1)
Wend
Print #2, chval, Asc(chval)
Close #1
Close #2
w Notice the difference in the line that reads the input file
v Look up Input function in online Help
v Study the example
v What is the difference between Input and Input # ?
{Notice that you can go from the one entry to the other
by clicking on
See Also}w Use online Help to learn about the ASCII character set
w Use that information to study your output file
w What is the 13-10 combination that appears repeatedly in that
file?