NWEN 241 Assignment 2

NWEN 241 Assignment 2
(Weeks 3–5 Topics)

In this assignment, you will be asked to implement C functions, the specifications of
which are presented in each of the tasks. To be submitted in file named dbms.c.
You must submit the required file to the Assessment System (https://apps.ecs.vuw.
ac.nz/submit/NWEN241/Assignment_2). Any assignment submitted up to 24 hours
after the deadline will be penalised by 20%, and any assignment submitted between 24
and 48 hours after the deadline will be penalised by 40%. Any assignment submitted 48
hours or more after the deadline will not be marked and will get 0 marks.
Important: The Assessment System is configured not to accept submissions that do not
compile. So please test that your code compiles using a C compiler before submitting it.
Full marks is 100. The following table shows the overall marks distribution:
Criteria Marks Expectations for Full Marks
Compilation 10 Compiles without warnings
Comments 10 Sufficient and appropriate comments
Coding Style 10 Consistent coding style
Correctness 70 Handles all test cases correctly (see
marks distribution below)
Total 100
For the Correctness criteria, the following table shows the marks distribution over the
different task types:
Task Type Marks
Core 45
Completion 15
Challenge 10
Total 70
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NWEN 241 2021-T1 (Weeks 3–5 Topics) Assignment 2
Introduction
This assignment will test whether you can apply the conceptual knowledge you have
learned in Weeks 3–5 to solve practical programming tasks. You must only use the
Standard C Library to perform the tasks in this part.
You will implement a simple database management system (DBMS). DBMS is a systems
program that performs storage, retrieval, and updating of data in a computer system.
DBMS addresses two major problems in conventional file-based systems: data
redundancy and data dependence.
Sample code showing an example on how you can test your code are provided under
the files directory in the archive that contains this file.
Commenting
You should provide appropriate comments to make your source code readable. If your
code does not work and there are no comments, you may lose all marks.
Coding Style
You should follow a consistent coding style when writing your source code. Coding style
(aka coding standard) refers to the use of appropriate indentation, proper placement of
braces, proper formatting of control constructs, and many others. Following a particular
coding style consistently will make your source code more readable.
There are many coding standards available (search "C coding style"), but we suggest you
consult the lightweight Linux kernel coding style (see https://www.kernel.org/doc/
html/v4.10/process/coding-style.html). The relevant sections are Sections 1, 2,
3, 4, 6, and 8. Note that you do not have to follow every recommendation you can find in
a coding style document, you just have to apply that style consistently.
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NWEN 241 2021-T1 (Weeks 3–5 Topics) Assignment 2
Program Design
A fundamental concept in DBMS is the table. A table consists of zero or more records or
entries, and each record can have one or more fields or columns. An example of a table
that stores information about music albums is shown below:
id title year artist
10 The Dark Side of the Moon 1973 Pink Floyd
14 Back in Black 1980 AC/DC
23 Their Greatest Hits 1976 Eagles
37 Falling into You 1996 Celine Dion
43 Come Away With Me 2002 Norah Jones
55 21 2011 Adele
This table contains 6 records. Each record has 4 fields, namely, id, title, year, and
artist.
In this assignment, you will focus on implementing a single database table with 4
fields (id, title, year, and artist). To guide you in the implementation, a high-level design
of the table is shown below:
The design consists of a db_table structure and an array of album structures that is
dynamically allocated. The db_table structure should have the following member
variables:
• table: a pointer to an array of structures that is dynamically allocated,
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NWEN 241 2021-T1 (Weeks 3–5 Topics) Assignment 2
• rows_total: the total number of rows in the array of structures,
• rows_used: the number of rows in the array of structures that contains valid
records.
The array of album structures will hold the records. This array should be dynamically
allocated and adjusted using the following scheme:
• Initially, the array should be empty. rows_total should be set to 0 and
rows_used should be set to 0.
• When adding a record and there is unused space in the table (rows_used is less
than rows_total), the record is stored in the next unused row, and rows_used is
updated accordingly.
• When adding a record and there is no space in the table (rows_used is equal to
rows_total), additional memory for holding 5 records should be allocated. Then,
the record is stored in the next unused row, and rows_used and rows_total are
updated accordingly.
• When removing a record, records after the removed record should be moved up by
one row so that there will be no gaps in between used rows. When the number of
unused rows reaches 5, the unused rows should be released, and rows_used and
rows_total are updated accordingly.
The definition of the db_table and album structures are given in the header file named
dbms.h which is provided under the files directory.
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NWEN 241 2021-T1 (Weeks 3–5 Topics) Assignment 2
Task 1.
Core [45 Marks]
Provide an implementation of a function called db_show_row for displaying the
information stored in a row. The display output should be formatted as follows:
id: title: artist:year
where id, title, artist, and year should occupy 6, 20, 20, and 4 spaces, respectively.
Shorter values should be padded with space, whereas longer values should be truncated
to fit within the space. As an example, for the record with id 10, title "The Dark Side
of the Moon", year 1973, and artist "Pink Floyd", the output should be
10:The Dark Side of the: Pink Floyd:1973
where represents a single space. There should be newline at the end of line.
The function prototype is given in the header file named dbms.h which is provided under
the files directory.
The function accepts two input parameters:
• Pointer to a db_table structure (see definition in dbms.h.)
• Unsigned integer indicating the row number of the record to be displayed.
If the record exists, the function should return 1, otherwise, it should return 0.
Save the function implementation in a C source file named dbms.c.
You can test your function implementation by compiling dbms.c together with the file
named t1test.c which is provided under the files directory. Read the contents of
t1test.c to know how to compile and run the resulting executable file.
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NWEN 241 2021-T1 (Weeks 3–5 Topics) Assignment 2
Task 2.
Completion [15 Marks]
Provide an implementation of a function called db_add_row for adding a record into the
database table. The function prototype is given in the header file named dbms.h which
is provided under the files directory.
The function accepts two input parameters:
• Pointer to a db_table structure (see definition in dbms.h.)
• Pointer to album structure (see definition in dbms.h) as input parameter containing
the record details to be stored in the table.
As mentioned in the Program Design section:
• When adding a record and there is unused space in the table (rows_used is less
than rows_total), the record is stored in the next unused row, and rows_used is
updated accordingly.
• When adding a record and there is no space in the table (rows_used is equal to
rows_total), additional memory for holding 5 records should be allocated. Then,
the record is stored in the next unused row, and rows_used and rows_total are
updated accordingly.
The function should always return 1 unless the allocation of additional memory (when
needed) fails where it should return 0.
Save the function implementation in a C source file named dbms.c.
You can test your function implementation by compiling dbms.c together with the file
named t2test.c which is provided under the files directory. Read the contents of
t2test.c to know how to compile and run the resulting executable file.
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NWEN 241 2021-T1 (Weeks 3–5 Topics) Assignment 2
Task 3.
Challenge [10 Marks]
Provide an implementation of a function called db_remove_row for removing a record
from the database table. The function prototype is given in the header file named dbms.h
which is provided under the files directory.
The function accepts two input parameters:
• Pointer to a db_table structure (see definition in dbms.h.)
• Unsigned long integer specifying the id of the record to be removed.
As mentioned in the Program Design section:
• When removing a record, records after the removed record should be moved up by
one row so that there will be no gaps in between used rows. When the number of
unused rows reaches 5, the unused rows should be released, and rows_used and
rows_total are updated accordingly.
The function should return 1 if the removal was successful, otherwise, it should return 0.
Save the function implementation in a C source file named dbms.c.
You can test your function implementation by compiling dbms.c together with the file
named t3test.c which is provided under the files directory. Read the contents of
t3test.c to know how to compile and run the resulting executable file.
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