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Assignment 4
CSCI 2132: Software Development
Due March 4, 2019
Assignments are due on the due date before 23:59. All assignments must be submitted electronically via the course SVN
server. Plagiarism in assignment answers will not be tolerated. By submitting your answers to this assignment, you declare
that your answers are your original work and that you did not use any sources for its preparation other than the class notes,
the textbook, and ones explicitly acknowledged in your answers. Any suspected act of plagiarism will be reported to the
Faculty’s Academic Integrity Officer and possibly to the Senate Discipline Committee. The penalty for academic dishonesty
may range from failing the course to expulsion from the university, in accordance with Dalhousie University’s regulations
regarding academic integrity.
General Instructions: How to Submit Your Work
You must submit your assignment answers electronically:
Change into your subversion directory on bluenose: cd ~/csci2132/svn/CSID .
Run svn update . This will create a directory a4 in your subversion directory. Inside this
directory, you will find a file genseq.c.
Change into your assignment directory: cd a4 .
Compile the genseq.c file to executable code using gcc -o genseq genseq.c . You will need
this program for the second question.
Create files inside the a4 directory as instructed in the questions below and put them under
Subversion control using svn add <filename> . Only add the files you are asked to add!
Once you are done answering all questions in the assignment (or the ones that you are able to
answer—hopefully all), the contents of your a4 directory should look like this:
a4
genseq.c
primetest.c
stats.c
(You will also have executable programs and potentially some data files in this directory, but you
should not add them to SVN.) Submit your work using svn commit -m”Submit Assignment 4″ .
1
(Q1) Primality Testing 10 marks
Recall that a number is a prime number if its only divisors are 1 and itself. Write a C program that
prints“Enter a number:”to stdout and reads an unsigned integer from stdin. (Use scanf to do
so. You do not need to perform any error checks.) Your program should print“x is a prime number.”,
where x is the number you entered, if x is a prime number. Otherwise, it should print“x is not a prime
number.”The exit code of your program should be 0.
For full marks, your program must meet the following requirements concerning the implementation:
? You should be able to handle any unsigned integer that fits in 64 bits.
? When testing whether there exists a number y that divides x (and, thus, x is not a prime number),
restrict yourself to integers y ≤ 2
p
x. Precisely, the largest number y you test whether it divides
x should be between p
x and 2
p
x. The logic is that, if there exists a number z ≥
p
x that divides
x, then x = yz for some number y ≤
p
x and y also divides x. The reason why the permissible
range of y is [2, 2p
x] is explained in the next bullet.
For full marks, find the maximum value of y you test without calling the sqrt library function
(which is a floating point function). Instead, use C’s bit shift operator to calculate the maximum
value of y you need to test. This may return a number as large as 2p
x.
Implement your program in a file primetest.c, place this file into your a4 directory and commit it to
SVN.
(Q2) Calculating the Distribution of Values 10 marks
For a set of n real numbers {x1
, . . . , xn
}, here are a number of basic statistics we would like to know
about the distribution of these numbers:
The minimum value m = min{x1
, . . . , xn}.
The maximum value M = max{x1
, . . . , xn}.
The average value a =1nPni=1xi.
The standard deviation s =q1nPni=1(xi a)2.
Write a program stats.c that calculates these values for a sequence of values it reads from stdin.
The input is provided as a sequence of n + 1 numbers, each on a separate line. The first number is n.
The remaining n numbers are x1
, . . . , xn
. Your program may assume that n ≤ 1000. For two bonus
marks, your code should be able to handle any value of n, even values greater than 1000.
For any given input, your program should print the output
2
to stdout, where the … are to be replaced with the values of m, M, a, and s. Each output value
should be represented with 3 digits after the decimal point.
To generate some test data for your program, you can use the genseq program you created earlier. The
invocation ./genseq <n> generates a sequence of n random numbers and prints n followed by these
n random numbers to stdout. Using ./genseq <n> > seq.txt , you can save this output in a file
seq.txt. You can use this as the test input for your stats program by running ./stats < seq.txt .
Add your file stats.c to SVN and commit it.
