Lecture 16
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Log into Windows/ACENET. Use a web
browser to download today's exercise program.
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Go to course webpage. Right-click on
RandomNumberProgram.zip link. Save target/link
to Documents -> Visual Studio 2010 -> Projects
folder.
Browse to RandomNumberProgram.zip, right-click
on it and select Extract All... and extract project
folder
Double-click into the RandomNumberProgram
folders to the solution file, then double-click it to
start up VS.
Wednesday, February 16
CS 205 Programming for the Sciences - Lecture 16
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Outline
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Reminder: Programming Assignment 4 due
today by 4:30pm
Array parameters and arguments
Finish last class' in-class exercise, start MSVS
again to open TestStatsProgram
Random numbers
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CS 205 Programming for the Sciences - Lecture 16
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In-class Exercise, Last Class
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Modify the Main method of the TestStats
program as follows:
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Replace the score variables with an array of 11
elements.
Replace the calls to GetTestScore with a for-loop
that calls GetTestScore for each array element.
Modify the computation of total to use the array
elements. (We will fix this later.)
Replace the calls to DisplayResultRow with a forloop that calls DisplayResultRow for each array
element.
Wednesday, February 16
CS 205 Programming for the Sciences - Lecture 16
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Array Parameters
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Just like other data items, arrays can be passed
to a method as a parameter. Unlike other data
items, arrays are always passed by reference,
and there is no special syntax for doing so.
The syntax for an array parameter is:
... <methodname> (<type> [ ] <arrayname>, ...)
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For example, a method ComputeAverage that
receives an array and returns the average of
the values in the array would have header:
static double ComputeAverage (double [ ] array)
Wednesday, February 16
CS 205 Programming for the Sciences - Lecture 16
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Array Arguments
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To call a method that has an array parameter,
the corresponding argument simply is the array
name. (That is, there are no square brackets or
size.)
In the example, to call ComputeAverage, we
would write:
average = ComputeAverage (score);
Wednesday, February 16
CS 205 Programming for the Sciences - Lecture 16
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In-class Exercise, Last Class
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Modify the TestStats program as follows:
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Add a method ComputeAverage that receives an
array of real numbers and returns the average of
the numbers in the array. The average should be
computed by using a for-loop to sum the elements
of the array together, then dividing by the number of
elements in the array.
At the beginning of the Main method, write code to
get the number of test scores from the user; change
the array creation to use this number for its size.
Replace the average-computing code in the Main
method with a call to ComputeAverage.
Wednesday, February 16
CS 205 Programming for the Sciences - Lecture 16
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In-class Exercise
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Today's exercise is to write several methods to
compute various statistical quantities. The
program will do the following:
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Ask the user for the number of values needed
Create an array of integers of that size
Fill the array with random integers in range [0..99]
Compute the minimum value in the array, the
maximum value in the array, the average of the
values in the array, and the standard deviation of
the values in the array
Displays these statistical quantities
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CS 205 Programming for the Sciences - Lecture 16
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RandomFillArray
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A method RandomFillArray that fills an array
with random integers is already written. This
method uses a variable num that is of type
Random. Like arrays, Random objects need
to be created using the new operator.
A Random object generates (pseudo)random
integers. These integers are returned by the
Next method that takes a lower and an upper
bound as arguments. The range of the
returned value is [lower..upper), i.e., the upper
end is open.
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CS 205 Programming for the Sciences - Lecture 16
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RandomFillArray
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This program declares the Random variable
num as a static class variable by putting its
declaration outside any method (but inside the
class) and prefixing the declaration with the
static modifier.
This is done so that there is only one Random
number generator in the program that is
accessible to all methods in the class. Also, the
random number generator will retain state
between method calls that use it, rather than
starting over each time it is created.
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CS 205 Programming for the Sciences - Lecture 16
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DisplayArray
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A method DisplayArray is already written.
This method displays an array of integers by
displaying 10 numbers on each line.
Note this is done by displaying each array
element using Console.Write( ) and a format
specifier with a field width of 4, and using the
modulus operator (%) to determine when a new
line needs to be started.
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ComputeMinimum
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A method ComputeMinimum is already
written. It has an array of integer parameter
and returns the minimum value in the array.
This is the way it is computed:
1. Declare an integer variable minimum and
initialize it to the first element of the array.
2. For each element after the first one
2.1 If the element is less than the minimum
2.1.1 The element becomes the new minimum
3. After the loop is finished, minimum is the smallest
value seen in the array, so return it.
Wednesday, February 16
CS 205 Programming for the Sciences - Lecture 16
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In-class Exercise
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Copy the ComputeAverage method from TestStats.cs
and paste it into this program. Modify it to use an
integer array parameter. Note that the sum should
remain a double variable to ensure real division in
computing the average.
In the Main method, do the following:
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Declare and create an array of integers of the size input by
the user.
Call the RandomFillArray method to fill the array with
random numbers and DisplayArray to display it.
Compute the mininum value and the average value by
calling ComputeMinimum and ComputeAverage,
respectively, and display these results.
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CS 205 Programming for the Sciences - Lecture 16
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In-class Exercise
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At this point, make sure your program compiles
and runs correctly. Use small values for the
user input so that you can hand compute
whether the minimum and average are
computed correctly.
The rest of the exercise is to write methods
ComputeMaximum, and ComputeStdDev,
which are described on the next slides. After
completing each method, you should make
sure your program compiles and runs correctly.
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ComputeMaximum
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ComputeMaximum basically is the same as
ComputeMinimum except that we are looking
for elements greater than the current maximum:
1. Declare an integer variable maximum and
initialize it to the first element of the array.
2. For each element after the first one
2.1 If the element is greater than the minimum
2.1.1 The element becomes the new maximum
3. After the loop is finished, maximum is the largest
value seen in the array, so return it.
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ComputeStdDev
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ComputeStdDev has an array of integers
parameter and also receives the average of
the values in the array. It computes and returns
the standard deviation of the values in the
array. The formula for standard deviation is:
S=
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n
∑  x i−avg2
i =1
n
Note that the summation is 1 to n, but that the
array indexes will be 0 to n-1.
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ComputeStdDev
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In the Main method, call this method and
display the result. Note that ComputeStdDev
must be called after the average has been
computed.
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