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# Project 1 - Matrix Class & Operator Overloading CSCI 1730  Solution

Your goal for this project is to create an easy-to-use Matrix class in C++ that makes use of dynamic memory allocation
and includes basic matrix operations both in the form of regular functions and via operator overloading. Certain aspects
of this project might be taught concurrently with the project. Other aspects of this project may not be covered in lecture.
You are encouraged to use the DEITEL text and cppreference.com as references. Also, please ask questions via Piazza.
Specifically, the following chapters from the textbook may be useful for this project:
• DEITEL 3.1–37 (pp. 73–102)
• DEITEL 8.1–812 (pp. 339–384)
• DEITEL 9.1–9.16 (pp. 385–433)
• DEITEL 10.9 (pp. 466–468)
Here is the basic prototype for the Matrix class (you may need to add more to it to support some of the additional features
listed further down in this document):
typedef unsigned int uint;
typedef initializer_list<initializer_list<double i_list;
class Matrix {
public:
Matrix(uint rows, uint cols); // constructor (all elements initialized to 0)
Matrix(const i_list & list); // constructor (using initializer list)
Matrix(const Matrix & m); // copy constructor
~Matrix(); // destructor
Matrix add(const Matrix & m) const; // add this matrix and another matrix
Matrix subtract(double s) const; // subtract scalar from this matrix
Matrix subtract(const Matrix & m) const; // subtract another matrix from this matrix
Matrix multiply(double s) const; // multiply this matrix by a scaler
Matrix multiply(const Matrix & m) const; // multiply this matrix by another matrix
Matrix divide(double s) const; // divide this matrix by a scalar
Matrix t() const; // transpose of this matrix
const uint numRows() const; // returns the number of rows
const uint numCols() const; // returns the number of cols
double & at(uint row, uint col); // get/set element at row,col
const double & at (uint row, uint col) const; // get element at row,col (when using a const object)
}; // Matrix

Important Class Details

Your Matrix implementation will contain elements of type double. In the prototype presented above, the term scalar refers
to a regular number. For example, if you add a scalar to a matrix, then each element in the matrix gets that number added
to it. Contrast this with the member functions that take a Matrix as their parameter. These functions represent regular
matrix operations. For some of these operations (e.g., multiplication, transpose, etc.), you may need to consult some sort of
reference in order to recall/learn the exact procedure/meaning behind the operation.

NOTE: You MAY assume valid input for all operations.
NOTE: You MAY NOT use library classes such as std::array, std::vector, std::list, etc. for this project. You must
implement your Matrix class internally using a dynamically allocated array.
Example Usage 1
Matrix a(2, 2);
a.at(0, 0) = 1; // [ 1, 2 ]
a.at(0, 1) = 2; // [ 1, 3 ]
a.at(1, 0) = 1;
a.at(1, 1) = 3;
Matrix b(2, 1);
b.at(0, 0) = 3; // [ 3 ]
b.at(1, 0) = 2; // [ 2 ]
Matrix c = a.multiply(b);
cout << "[ " << c.at(0, 0) << " ]" << endl // [ 7 ]
<< "[ " << c.at(1, 0) << " ]" << endl; // [ 9 ]
Matrix d = {{1, 2}, // this will implicitly call the overloaded constructor
{3, 4}}; // that takes an initializer list
The usage of the member function at(uint, uint) is what facilities our ability to perform operations such as a.at(0, 0)
= 1. If you implement this function carefully, then this behavior should work because the function returns a reference to an
element. In order to support the constructor overload (i.e., matrix construction using an initializer list), you will need to use
a standard template library (STL) class called std::initializer list1
. The type signature for the constructor parameter
representing the list should be std::initializer list<std::initializer list<double or simply i list if you use the
provided typedef.

You will also need to overload operators in order to support the following functionality. It is up to you whether or not these
should be member or non-member overloads.
// assume we have two matrices of appropriate size already set up
Matrix a;
Matrix b;
// after providing the overloads, you should be able to do any of the following operations
// using regular operators instead of the member functions
Matrix c0 = a + 5.2;
Matrix c1 = a + a; // NOTE: these examples actually end up calling the copy constructor
Matrix c2 = a - 3.5; // e.g., this line is the same as Matrix c2(a - 3.5);
Matrix c3 = b - b;
Matrix c4 = a * 2.1;
Matrix c5 = a * b;
Matrix c6 = a / 2.0;
1std::initializer list: http://en.cppreference.com/w/cpp/utility/initializer_list

You should also support stream insertion (similar to overriding the toString method in Java) so that your matrices can
easily be printed.
cout << a << endl; // example output: [ 1, 2 ]
// [ 1, 3 ]
You should also support matrix assignment using an initializer list (to easily overwrite existing elements) that looks like the
following:
Matrix d(2, 2);
d = {{ 1, 2 },
{ 3, 4 }};
In order to support this last operator overload (i.e., matrix assignment using an initializer list), you will need to use a standard
template library (STL) class called std::initializer list. The type signature for the << parameter representing the list
should be std::initializer list<std::initializer list<double or simply i list if you use the provided typedef.
It is preferred that you specify the parameter as a const i list & in order to avoid any unnecessary copying.
In addition to the requirements for listed above, you need to make sure your Matrix class supports the following features:
• Overloaded Function Call Operator (operator()(uint row, uint col)): After creating a Matrix object, the
user should be able to access the elements using the function call operator (as an alternative to using the at function):
Matrix a(1, 1);
a(0, 0) = 5;
cout << a(0,0) << endl;
the assignment operator to take in a special kind of initializer list. Now you need to provide an additional overload
that supports copy assignment. This will make your Matrix class more consistent since copy assignment parallels copy
construction. Here is an example:
Matrix a(1, 1);
a(0, 0) = 5;
Matrix b(1, 1);
b = a; // copy assignment
support the basic arithmetic operations where the right-hand-side of an operation is a scaler value. Now you need to
implement operator overloads so that scalers can be used on the left-hand-side of an operation. Here is an example
showing the operators that you need to support:
Matrix a = {{1, 2},
{3, 4}};
Matrix b = 4.0 + a; // [ 5, 6 ]
// [ 7, 8 ]
Matrix c = 4.0 - a; // [ 3, 2 ]
// [ 1, 0 ]
Matrix d = 2.0 * a; // [ 2, 4 ]
// [ 6, 8 ]
Matrix e = 12.0 / a; // [ 12, 6 ]
[ 4, 3 ]
• Overloaded Unary Minus Operator (operator-()): You need to support negating your Matrix objects:
Matrix a = {{1, 2}};
cout << -a << endl; // [ -1, -2 ]
3
1 C++ Code & Program

1.1 Setup

Make sure that all of your files are in a directory called LastName-FirstName-p1, where LastName and FirstName are
replaced with your actual last and first names, respectively.

1.2 Source Code Files

You should organize your project into the following files:
• Matrix.h: This file should include the class prototype presented above as well as the prototypes for operator overloads
that you implement. You MAY NOT modify the function prototypes that are included in the Matrix class prototype.
However, you may add additional function prototypes and variables to the class prototype as needed. Make sure that
this header file also includes a header guard (i.e., the #ifndef macro, etc.).
• Matrix.cpp: This file should contain the implementation of your class’s functions as well as the implementation of any
• p1.cpp: This file should contain a small/moderately sized driver that demonstrates the full range of functionality of
• All functions must be documented using Javadoc-style comments. Use inline documentation, as needed, to explain
ambiguous or tricky parts of your code.

1.3 Makefile File

You need to include a Makefile. Your Makefile needs to compile and link separately. Make sure that your Matrix.cpp file
compiles to Matrix.o. This is very important because we will be testing your submission by linking against your Matrix.o
file. The resulting executable should be called p1.
Make sure that when you compile, you pass the following options to g++ in addition to the -c option:
-Wall -std=c++14 -g -O0 -pedantic-errors

Make sure to include a README file that includes the following information presented in a reasonably formatted way:
• Instructions on how to compile and run your program.
NOTE: Try to make sure that each line in your README file does not exceed 80 characters. Do not assume line-wrapping.
Please manually insert a line break if a line exceeds 80 characters.

1.5 Compiler Warnings

Since you should be compiling with both the -Wall and pedantic-errors options, your code is expected to compile without
g++ issuing any warnings. For this project, compiling without warnings will be one or more of the test cases.

1.6 Memory Leaks

Since this project makes use of dynamic memory allocation, you are expected to ensure that your Matrix implementation
doesn’t result in any memory leaks. We will test for memory leaks using the valgrind utility. For this project, having no
memory leaks will be one or more of the test cases.