ENGR/CS 101 CS Session
Lecture 16
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Log into Windows (reboot if in Linux)
Use web browser to go to session webpage
http://csserver.evansville.edu/~hwang/f13-courses/cs101.html
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Right-click on Inclass16.zip link. Save link/target
to Visual Studio 2012 Projects folder (or
wherever the others are).
Browse to Inclass16.zip, right-click on it and
select Extract All... and extract project folder
Browse to the extracted folder, double-click into
the Statistics folder to the solution file.
Lecture 16
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Outline
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Arrays
Finding minimum and maximum values
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Storing Collections
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Last class we discussed searching and
sorting algorithms. Today we will discuss
how the data storage might be arranged.
First, we want the data to be stored in a
collection that is arranged to allow us easy
access to each element.
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.
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Arrays
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In C#, array variables are declared using the
following syntax, where <type> is the type of
the elements:
<type> [] <name>;
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As with other object types, arrays must be
created. The syntax for this is as follows,
where <size> is the number of elements:
<name> = new <type> [<size>];
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Arrays
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To access an array element, you give the
array name and the index of the element.
Almost all programming languages (including
C#) use:
<array name>[<index>]
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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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Statistics Project
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If you have not already done so, browse to
the Statistics project folder and double-click
on the solution file.
Statistics is an application that we can use to
explore arrays and algorithms that use them.
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Interface Mockup
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The Load button will
load a file into the left
TextBox called
displayBox. It has a
scrollbar to allow any
number of items.
The project has a file
random_numbers.txt
containing these
numbers.
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Interface Mockup
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Each of the other buttons will be used to
compute a statistic of the numbers loaded
from the file.
The result is then displayed in the textbox
next to the button. They are named
minimumBox, maximumBox, averageBox,
and stddevBox, respectively.
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Textbox as an Array
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Double-click on the Load button. This should
take you to its handler, which is partially
written. The display textbox is loaded as a
single string was done in the previous project.
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 display as displayBox.Lines[0].
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Creating an Integer Array
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In order to compute statistics on the data, we
must convert the strings in the display into
integers.
First we need to declare an integer array.
int [] items;
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Then we need to create the array after we
know how many items there will be in the
Load button handler.
items = new int [num_items];
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Filling the Array
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To fill the array, we need to access the
display lines one at a time using a for-loop.
For each line, we compute the equivalent
integer and store it in the items array.
for (int i = 0; i < num_items; i++)
{
items[i] =
Int32.Parse(displayBox.Lines[i]);
}
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Finding the Minimum Value
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In the Minimum button handler, we write the
code for finding the minimum value in the
items array.
The basic idea is to go through the array
keeping track of the current minimum value.
Start by assuming the first element is the
minimum value.
Use a for-loop and an if-statement to check
the rest of the elements.
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minimumBtn_Click code
// assume first item is min
int min = items[0];
// look at the rest of the items
for (int i = 1; i < num_items; i++)
{
if (items[i] < min) // a new min
min = items[i];
}
// display the result
minimumBox.Text = min.ToString();
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In-class Exercise
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Run the program and make sure that it
reports the minimum value.
Double-click on the Maximum button. Write
the handler code to determine the maximum
value in the items array and display it in the
maximum textbox. Hint: how does this differ
from finding the minimum value?
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