INPUT
AND
OUTPUT
1
OUTPUT
TextBoxes & Labels
MsgBox Function/Method
MessageBox Class
Files (next topic)
Printing (later)
2
MsgBox
MsgBox (text [,buttons [, caption/title]]) As MsgBoxResult
MsgBox(“You must provide a file name”,,”File Error”)
To learn more about
MsgBoxes, use Help.
3
MsgBox
MsgBox (text [,buttons [, caption/title]]) As MsgBoxResult
response = MsgBox(“Incorrect name-Continue?”,
4+32,”File
Error”)
CType(4+32,MsgBoxStyle),”File
Error”)
When casting using CInt, we know the result will be an Integer.
However, when using CType, the type is listed as the last parameter.
Using numerical values is rather cryptic.
4
MsgBox
response = MsgBox(“Incorrect name-Continue?”,
CType(4+32,MsgBoxStyle),”File Error”)
Instead of using the numerical values, we will use VB
constants:
response = MsgBox(“Incorrect name-Continue?",
y,
"File Error"))
MsgBoxStyle.YesNo,"File
MsgBoxStyle.YesNo+,"File
MsgBoxStyle.YesNo+MsgBoxStyle.Question,
Ctype(MsgBoxStyle.YesNo+MsgBoxStyle.Question,
Error")
Error")
"File Error")
MsgBoxStyle),"File
Error")
Now let’s look at the value for response.
5
MsgBox
response = MsgBox(“Incorrect name-Continue?”,
CType(MsgBoxStyle.YesNo+MsgBoxStyle.Question,
MsgBoxStyle),"File Error")
vbNo)
Then
If(response = 7)
Then
... ...
Now we have some code that is more
understandable—Yes and No buttons,
a Question mark icon, and we are
checking for a negative response.
6
MessageBox
MessageBox.Show (text [ ,caption/title [,buttons [, icon[
,defaultbutton]]]])
MessageBox.Show("You must provide a file name",
"File Error",MessageBoxButtons.OK)
To learn more about
MessageBoxes, use Help or
see pages 320-321 in the text.
7
INPUT
Textboxes
InputBox Function/Method
Files (next topic)
8
InputBox
InputBox ( Prompt As String[, Title As String][, DefaultResponse
As String][, XPos As Integer][, YPos As Integer]) As String
fileName =
If the user clicks OK, fileName will be grades. xlsx, and
InputBox("You
mustCancel,
provide
a file
if the user clicks
fileName
will bename",
the empty "File
string.
Error")
To learn more about
InputBoxes, use Help.
9
Accessing
Files
10
Access Methods
1.
Sequential Access Method (SAM)
2.
Direct (Random) Access Method (DAM)
3.
Indexed Sequential Access Method (ISAM)
11
Accessing Files
1.
We are going to limit our work with
files and only use the Sequential
Access Method (SAM)
2.
Text Files (which we will discuss)
3.
Binary Files (which we will not discuss)
12
Steps needed to transfer
data to/from files
1. Include necessary libraries
2. Declare a file stream object
3. Open the file stream
4. Transfer the data
5. Close the file stream
13
SAM with Text Files
Using the FileStream Class
Before we can transfer data from a text file, we have to
know how it is arranged. For our first example, the data
are listed one measurement per line.
When accessing a file, if no path is specified,
then the file must be in the debug subfolder.
14
C++
VB
#include <fstream.h>
ifstream inFile;
inFile.open(“measures.txt”);
.
.
.
inFile.close();
I/O is one of the areas in
which c and c++
are different!
Imports System.IO
Dim inFile As StreamReader
inFile = File.OpenText
(“measures.txt”)
.
.
.
inFile.close()
This will cause an error if the file does not
exist. We will address trapping errors or
catching exceptions in the next slide show.
15
C++
VB
#include <fstream.h>
ofstream outFile;
outFile.open(“results.txt”);
.
.
.
outFile.close();
Imports System.IO
Dim outFile As StreamWriter
outFile = File.CreateText
(“results.txt”)
.
.
.
outFile.close()
To add to an existing file, you would use
File.AppendText
16
Let’s put the two previous
slides together and create
a program the reads data
from a file, performs a
calculation, and writes the
result to another file.
17
C++
VB
#include <fstream.h>
ifstream inFile;
inFile.open(“measures.txt”);
ofstream outFile;
Why are
outFile.open(“results.txt”);
.
.
.
Assume that we have:
int
inFile >> length;
int
inFile >> width;
int
area=length*width;
outFile << area <<
.
.
.
inFile.close();
outFile.close();
Imports System.IO
Dim inFile As StreamReader
Dim outFile As StreamWriter
inFile = File.OpenText
these needed? (“measures.txt”)
outFile = File.CreateText
(“results.txt”)
.
.
.
length;
width;
area;
Dim length As Integer
length = Cint(inFile.Readline)
Dim width As Integer
width = Cint(inFile.ReadLine)
Dim area As Integer
area = length * width
endl;
outFile.WriteLine(area.ToString)
.
.
.
NOT needed, the Write
and WriteLine
inFile.close()
methods are “overloaded.”
outFile.close()
What other code must we
add to this program?
18
Although we could use a For-Loop
why is this inappropriate?
Imports System.IO
.
.
.
Dim inFile As StreamReader
Dim outFile As StreamWriter
inFile = File.OpenText
(“measures.txt”)
outFile = File.CreateText
(“results.txt”)
For
i = 1 (inFile.Peek
To 3
Do While
<> -1)
length = Cint(infile.Readline)
width = Cint(infile.ReadLine)
area = length * width
outFile.WriteLine(area)
Next
Loop i
Assume that we have:
inFile.close()
Dim i As Integer
outFile.close()
19
How Are Imported Text Files Delimited?
20
Although the previous example works, I think of the
input file as:
Space delimited
Tab delimited
Comma delimited
Unlike
theusing
text,
am
using
comma
delimiters.
If we
were
a Idata
file
containing
name address
city stateSuch
zip,
and the
output
file
looking
like:
why would to
thisas
be aCSV
poor choice
for a delimiter?
files are referred
– Comma
Separated Values.
Let’s look at the code necessary to use a CSV file.
21
Before writing the code we need to examine a
method and a function
• The Split method is defined on page 281and returns
an array of strings, where each element contains a
substring of the original string
• Split (split character)
… name.Split (CChr(" "))
Strings are usually stored with a string count header and then the
string. For example “Tony” is stored as 4 T o n y and “Z” is stored
as 1 Z . The character Z is stored as just Z . Consequently, we must
cast the string into a character. In a like manner, if we are using a
space “ “, we must cast it into a character.
22
Consider the following example:
Dim name, first, middle, last As String
Dim fields(2) As String
name
Anthony Joseph Nowakowski
first
name = "Anthony Joseph Nowakowski“
Anthony
fields = name.Split(CChar(" "))
middle
first = fields(0)
middle = fields(1)
last = fields(2)
Joseph
last
Nowakowski
fields
Anthony
Joseph
Nowakowski
23
Before writing the code we need to examine a
method and a function
• The Split function is defined on page 291 and returns
an array of strings, where each element contains a
substring of the original string
• Split (string [,delimiterString] [,limit])
… Split(name)
If the delimiter is omitted, then a space is used.
If the limit is omitted then, all substrings are returned.
24
Before writing the code we need to examine a
method and a function
Consider the following example:
Dim name, first, middle, last As String
Dim fields(2) As String
name = "Anthony Joseph Nowakowski"
fields = Split(name)
first = fields(0)
middle = fields(1)
last = fields(2)
25
We now modify the code for the CSV example
Imports System.IO
.
.
.
Dim record, fields(1) As String
Dim inFile As StreamReader
Dim outFile As StreamWriter
inFile = File.OpenText
(“measures.csv”)
outFile = File.CreateText
(“results.csv”)
Do While (inFile.Peek <> -1)
record = infile.ReadLine These create a new CSV file.
fields = Split(record,”,”)
length = Cint(fields(0))
width = Cint(fields(1))
area = length * width
outFile.Write(length & ”,”)
outFile.Write(width & ”,”)
outFile.WriteLine(area)
Loop
inFile.close()
outFile.close()
26
Our final text example involves
the Gettysburg Address
Using the “traditional” format. i.e.
paragraphs indented and no doublespacing between paragraphs.
27
Our final text example involves
the Gettysburg Address
Text Box or Label?
Imports System.IO
.
.
.
Dim inFile As StreamReader
inFile = File.OpenText("GBA.txt")
txtGB.Text = inFile.ReadToEnd
lblGB.Text
inFile.Close()
28
Some Other Considerations
• What happens if we used the newer format? i.e. no
indentation with double-spaced paragraphs.
• Instead of using ReadToEnd, what would happen if
we used ReadLine to read each paragraph?
– The tabbed format is easier to implement.
29
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