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ENSF 619
Lab 4
Important Note: This is another individual lab assignment
This is another important lab assignment and it is aimed to help you understanding very essential topics such as
dynamic allocation of memory in C++, and concepts such as copying objects in C++.
Due Date: Friday Oct 16, before 5:00 PM
Marking scheme
• Exercise A 16 marks
• Exercise B 4 marks
• Exercise C 4 marks
• Exercise D Not marked
Exercise A: Design A Dynamic Array Class
Read This First:
This exercise is designed to give you some insight about a resizable array class. It also shows other feature of
C++ including proper way of copying objects of this class.
What to do:
Download files in the files MyArray.h and lab4ExA.cpp. Then read the file MyArray.h, which tells you what
the MyArray class interface is and what the member variables are. Pay close attention to the comment that
describes the memory management strategy for the MyArray class.
Read the file lab4ExA.cpp, which demonstrates how a MyArray object could be used.
The file MyArray.cpp is missing. It’s your job to write this file.
What to Submit:
Submit your file MyArray.cpp and your program output as part of your lab report
Exercise B: Using C++ library classes, vector and string
The objective of this exercise is to gain some experience in understanding the C++ library classes, vector,
and string.
What to Do:
Download the files lab4ExB.cpp from D2L. In this file there is a declaration of vector <string>. If you
compile and run this program it creates the following output:
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ABCD
EFGH
IJKL
MNOP
QRST
Let’s visualize this output as a matrix of letters (5 rows and 4 columns):
A B C D
E F G H
I J K L
M N O P
Q R S T
Your job is to complete the definition of the function called transpose that creates a new object of
vector<string> where its strings are the transpose of the original vector:
A E I M Q
B F J N R
C G K O S
D H L P T
To test your program, you can change the values of the constants ROWS and COLS, in the main function to make
sure your function works with other sizes of the String_Vector.
What to Submit:
Submit the definition of your function transpose and the program’s output.
Exercise C: C++ File I/O
The objective of this exercise is to help you understanding the basics of file I/O in C++.
What to Do:
Download the files lab4ExC.cpp from D2L. If you read this file carefully you will realize that this simple C++
program creates a binary file (for example: cities.bin), that contain several records of type struct City.
Each record has two double types represent x and y coordinates of a city on Cartesian Plan, followed by the
name of the city, which is stored as a C-string in an array of characters with 30 elements. The program has
several functions, the implementation of one of them, called print_from_binary, is missing. Your task will be
to write the definition of the missing function. This function is supposed to read the content of the binary file
created by the program, and display the its content (records both on the screen and into a text file, using in the
following format:
Name: Calgary, x coordinate: 100, y coordinate: 50
Here is the functions prototype and interface comment:
void print_from_binary(char* filename);
/* PROMISES: uses ifstream library object to open the binary file named
* “filename”, reads the content of the file which are objects of struct City
* (one record at a time), and displays them on the screen. It also saves the records
* into a text-file that its name must be filename argument, but with the extension of .txt
*/
What to Submit:
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Submit the definition of your function print_from_binary and the content or the generated text file, as part
of your lab report in PDF format.
Exercise D: Array of Pointers and Command Line Arguments
Read This First
Up to this point in our C and C++ programs, we have always used main functions without any arguments. In
fact, both languages, allow us to write programs that their main functions receives arguments. Here is the
heading of such a function:
int main(int argc, char **argv){ … }
Of course, we never call a main function from anywhere in our program, and we never pass arguments to it. A
main function can only receive its arguments from command line. In other words, when a user runs the program
from command-line, he/she can pass one or more arguments to the main. Good examples of this type of
programs are many of the Linux and Unix commands such as: cp, mv, gcc, g++. For example, the
following cp command receives the name of two files, to make file f.dat a copy of file f.txt:
cp f.txt f.dat
The first token in the above cp command is the program’s executable file name, followed by two file names. This
information will be accessible to the main. How does it work? Here is the answer:
To access the command-line arguments, a C/C++ main function can have arguments as follows:
#include <iostream>
using std::cerr;
int main(int argc, char **argv) {
if(argc != 3) {
cerr << “Usage: incorrect number of argument on the command line…\n””;
exit(1);
}
// MORE CODE AS NEEDED.
return 0;
}
Where, argc is the number of tokens on the command-line. In our cp command example, the value of argc
should be always 3 (one for program name and two for the file names). If the value of argc is not 3, the program
terminates after giving an appropriate message. In other words, this argument is mainly used for error-checking
to make sure user has entered the right number of tokens on the command line. The delimiter to count for the
number of tokens on the command- line is one or more spaces. The second argument is a pointer-to-pointer,
which points to an array of pointers. Each pointer in this array points to one of the string tokens on the command
line. The following figure shows how argv[0], argv[1], and argv[2] point to the tokens on the command
line:
The following code shows how you can simply access and display the command line strings in a C++ program:
cout << “The program name is: ” << argv[0] << endl;
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cout << “The first string on the command line is: ” << argv[1] << endl;
cout << “The second string on the command line is: ” << argv[2] << endl;
And, here is the output of this code segment for our cp command example:
The program name is: cp
The first string on the command line is: f.txt
The second string on the command line is: f.dat
The exact location of the memory allocated for command-line arguments depends on the underlying OS and the
compiler, but for most of the C/C++ systems it is a special area on the stack that is not used for the activation
records.
Read This Second
Since this part of exercise B deals with the command line entries by the user, you are strongly recommended to
implement, compile and run the program on a Cygwin terminal or Mac terminal.
You may be interested in knowing whether it is possible to pass command-line arguments to your program from
inside an IDE environment such as Visual C++ or XCode. The answer is yes! It is possible.
Most of the commonly used IDEs provide some way of entering the command line arguments into C/C++ project.
For example, in the newer versions of the XCode for the Mac computers, you can click on the ‘Edit Scheme’,
under the ‘Product’ menu option, and enter the command line argument strings on the ‘arguments’ tab. A similar
way is also available in Visual Studio: Right-click on the project, then select ‘Properties’ -> Debugging, and enter
your arguments into the arguments box. If you choose to use this option, you should seek for more details by
consulting the help options available on your target IDE, or search on the Internet.
Our experience shows, using the command line argument from inside some of the IDEs is not always
straightforward and figuring out how exactly it works, can be sometimes time-consuming.
What to Do:
Download the file lab4ExD.cpp from D2L. This is a simple program that uses the insertion-sort algorithm to
sort an array of integer numbers. Now, you should take the following steps:
1. Read the given program carefully to understand what it does.
2. If you are working from ICT lab (which is recommended), compile the program from Cygwin terminal
using the following command to create an executable file called sort:
g++ –Wall lab4ExD.cpp –o sort
3. Run the program using the following command:
./sort
It should print the list of several integer numbers, followed by the same list, sorted in ascending order.
4. Now change the value of the local variable sort_order from 1 to 2, recompile the program, and run it
again. Now it should sort the array in descending order.
5. Your task from this point is to modify the main function to have access to the command line
arguments. We want to be able to run the program with the options of sorting the numbers either in
ascending or descending order, based on the user’s input on the command-line.
Considering that the program’s executable name is sort, users must be able to run the program from
the command-line in one of the following formats:
./sort -a
Or:
./sort -d
In the first command the option –a (no spaces between dash and a) stands for the ascending, and the
second command with the option –d stands for the descending order.
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Depending on the user’s selection of one of these options, the program must sort an array accordingly.
To be more precise, the main function in this program must check the following conditions:
– If argc > 2 the program should give the following message and terminate:
Usage: Too many arguments on the command line
– If argc == 1, (meaning that the user didn’t enter any of the two options), the program should
use ascending sort as its default order.
– If argv[1], is NOT one of the following: –a, -A, -d, or –D, the program should give the
following message and terminate:
Usage: Invalid entry for the command line option.
Then, the program should:
– Set the value of sort_order to 1, if argv[1] points to the C-string: “–a” or “-A”.
– Set the value of sort_order to 2, if argv[1] points to the C-string: “–d” or “-D”.
Note: as you should recall from material discussed earlier in the course, you cannot compare C-strings by simply
using relational operators. Therefore, you need to call C library function strcmp. You may refresh your memory
regarding this function by reading your course notes, any of your textbooks, or an online sources such as
cplusplus.com at: http://www.cplusplus.com/reference/cstring/strcmp.
What to Submit:
As part of your lab report, submit your lab4ExE.cpp file and the output of the program that shows sorting the
array in ascending and descending orders.

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