ENGR/CS 101 CS Session
Lecture 11
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Log into Windows (reboot if in Linux)
Use web browser to go to session webpage
http://csserver.evansville.edu/~hwang/f12-courses/engrcs101/cs.html
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Right-click on Inclass11.zip link. Save link/target
to Visual Studio 2010 projects folder (or
wherever the others are).
Browse to Inclass11.zip, right-click on it and
select Extract All... and extract project folder
Double-click into the NameSearch folder, then
double-click on the Visual Studio Solution file.
Lecture 11
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Outline
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Arrays
Files
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OpenFileDialog
StreamReader
Design of linear search
Implementing linear search
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Lecture 11
While-loops
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Storing Collections
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Last class we discussed searching and
sorting algorithms. Today we will discuss
what we need to implement these algorithms.
First, we need a place to store the collection
of data. We want this storage arranged to
allow us to access each element easily.
Also, we want to be able to identify an
element of the collection by using the position
(or index) of the element in the collection.
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Arrays
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The simplest collection in most programming
languages is the array.
Formally, an array is an ordered collection of
elements of the same type that is accessed
by an index. Ordered means that the relative
position of each element matters.
To access an array element, you give the
array name and the index of the element.
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Arrays
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Almost all programming languages (including
C#) use
<array name>[<index>]
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as the syntax for accessing an array element.
Note this is the same syntax we used to
access an individual character in a string.
You can think of a string as a special kind of
array.
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Arrays
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The indexes of an array usually start at 0 or
1. For technical reasons, most modern
programming languages (including C#) start
indexing at 0.
Here is a picture of an array of 10 integers:
anArray
23 45 76 39
5
87 16 92 54 63
[0] [1] [2] [3] [4] [5] [6] [7] [8] [9]
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Interface Mockup
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NameSearch is a GUI
project that we can
use to explore arrays
and the linear search
algorithm.
The Load button will
load a file into the
large TextBox called
nameBox.
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Interface Mockup
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A string can be entered in the small textbox
called target. Clicking on the Search button
will search for the target Text in the lines of
nameBox.
If the target string is found, its position/index
will be displayed in the label named
resultLabel. If the target string is not found,
"-1" will be displayed.
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Reading from a File
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The click handler for the Load is already
written. The design of the handler is as
follows:
1. Create an OpenFileDialog object
2. Make the dialog pop up and wait for the user to
respond
3. Check if user canceled. If so, go back to waiting.
4. Attach the chosen file to a StreamReader object
5. Read the contents of the file and store it into the
name box.
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OpenFileDialog
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An OpenFileDialog is the window that pops
up when a user wants to open a file.
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StreamReader
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A file stream is a program object that is
opened (i.e., attached to a physical file) when
it is created. StreamReader objects are used
to read data from a file.
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There are also SaveFileDialog and
StreamWriter objects for writing data into a
file.
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Design of Linear Search
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Recall that the linear search algorithm is to start
at one end of a collection and check if each one
is the target item, stopping when the target is
found.
The result of doing a linear search often is the
index of the target element in the collection that
is then used to access other data or to do other
computations. For this project we will just
display the index of the target, if found.
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Design of Linear Search
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As noted previously, the data collection we will
be working with is the lines of text in the
nameBox. The Load button click handler treats
the Text property as one string.
C# also allows this data to be viewed as an
array of strings where each element is a line of
the text. The name of this property is Lines. So
for example, we can access the first line of the
nameBox as nameBox.Lines[0].
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Design of Linear Search
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Other data items that we need are
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Lecture 11
position – an integer that is the index of the target
element in the collection
found – a boolean flag that is used to stop the
search when the target is found
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Design of Linear Search
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Here is the full algorithm for the Search
button click handler:
1. Initialize position to 0 and found to false
2. While position is less than the length of list of names and
the target has not been found do
2.1 If nameBox.Lines[position] equals target string then
2.1.1 Set found to true
Else
2.1.2 Increment position
3. If target has been found then
3.1 Set the result label to position as a string
Else
3.2 Set the result label to "-1"
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While-Loops
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For indexing a string in the cipher project, we
know how many times we want to repeat the
encipher action, so we used a for-loop
We don't know when the searching loop will find
a match, so we need to use a while-loop to
implement this behavior.
The syntax for the while loop is:
while (<condition>)
{
// do something
}
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While-Loops
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The condition of the while-loop is tested and if it
is true, the body of the loop is executed. When
the condition becomes false, execution
continues with the statement after the loop.
For our program, we want the loop to stop if it
has checked every string in the nameBox.Lines
array or if a match is found. We can do this with
the following condition:
while (position < nameBox.Lines.Length
&& !found) // both must be true to repeat
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Implementing Linear Search
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Double-click on the Search button to get to
the click handler code stub for this button.
Write the code on the following two slides in
the searchBtn_Click handler. It implements
the design on Slides 14 and 15.
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Implementing Linear Search
// Declare and initialize variables
int position = 0;
// index of the target
bool found = false;
// flag to indicate target found
// while we haven't reached the end of the list
// and the target is not found
while (position < nameBox.Lines.Length && !found)
{
// check if the target is at this position
if (nameBox.Lines[position] == target.Text)
found = true;
else // it's not so try the next element
position++;
}
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Implementing Linear Search
// see if the target was found
if (found) // display its position as a string
resultLabel.Text = position.ToString();
else
// otherwise display "-1"
resultLabel.Text = "-1";
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Exploring Search Application
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When you have finished implementing the
linear search algorithm, run the application
with various search targets.
E.g., what happens if you search for "Cody"
(without the quotes)? For "Mary"? For
"kevon"? Why does "kevon" have a result of
-1?
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