C++ Programming Homework 7 Solution

● Define a template class Matrix that behaves like a two dimmensional array. I'll
outline it here for you, but you'll have to do all the C++ specific implementation.
Define each template class in a .h file with the same name as the class. Do not
define a .cpp file for either of the template classes. Define the methods inside the
class declaration (not separately down in the .cpp file as we have been doing for
non-template classes). REMEMBER: DO NOT COPY AND PASTE ANY CODE
BECAUSE YOU ARE STILL LEARNING THE LANGUAGE.
● (30 points) Convert the following class Array into a template where the element
type is a template parameter. Define it in a file Array.h with the method definitions
inside the class declaration. Be sure you know what all the iomanip objects do in
the print function (and know how to use them). A final quiz question depends on
your knowing and understanding them.
#include <cassert
class Array
{
private:
int len;
int * buf;
public:
Array( int newLen )
: len( newLen ), buf( new int[newLen] )
{
}
Array( const Array & l )
: len( l.len ), buf( new int[l.len] )
{
for ( int i = 0; i < l.len; i++ )
buf[i] = l.buf[i]; // note = is incorrect if buf
elements are pointers
}
int length()
{
return len;
}
int & operator [] ( int i )
{
assert( 0 <= i && i < len );
return buf[i];
}
void print( ostream & out )
{
for (int i = 0; i < len; ++i)
out << setw(8) << setprecision(2) << fixed << right <<
buf[i]; // #include <iomanip
}
friend ostream & operator << ( ostream & out, Array & a )
{
a.print( out );
return out;
}
friend ostream & operator << ( ostream & out, Array * ap )
{
ap-print( out );
return out;
}
// note the overloading of operator << on a pointer as
well
};

● (30 points) Write the following class Matrix as a template where the element type is a template parameter. Define it entirely in Matrix.h similar to how you did for template class Array.
class Matrix
{
private:
int rows, cols;
// define m as an Array of Array pointers using the
// template you defined above
public:
Matrix( int newRows, int newCols )
: rows( newRows ), cols( newCols ), m( rows )
{
for (int i = 0; i < rows; i++ )
m[i] = new Array < Element ( cols );
}
int numRows()
{
return rows;
}
int numCols()
{
return cols;
}
Array < Element & operator [] ( int row )
{
return * m[row];
}
void print( ostream & out )
{
// write this one too, but use Array::operator<<
}
friend ostream & operator << ( ostream & out, Matrix & m )
{
m.print( out );
return out;
}
};

● (20 points) Ensure your Matrix works correctly with the following main function.
Define main in main.cpp which includes Matrix.h. Test Matrix with at least two
different element types (e.g., int and double). I sketched the program below off the top of my head (without compiling), so there may be some errors, but it will be
good practice for you to eliminate them.
template
< typename T
void fillMatrix( Matrix <T & m )
{
int i, j;
for ( i = 0; i < m.numRows(); i++ )
m[i][0] = T();
for ( j = 0; j < m.numCols(); j++ )
m[0][j] = T();
for ( i = 1; i < m.numRows(); i++ )
for ( j = 1; j < m.numCols(); j++ )
{
m[i][j] = T(i * j);
}
}
void test_int_matrix()
{ // here is a start, but make it better
Matrix < int m(10,5);
fillMatrix( m );
cout << m;
}
void test_double_matrix()
{ // here is a start, but make it better
Matrix < double M(8,10);
fillMatrix( M );
cout << M;
}
int main()
{
test_int_matrix();
test_double_matrix();
return 0;
}

● (20 points) Define an exception class, IndexOutOfBoundsException, and have
your Array and Matrix class throw an instance of it if any index is out of bounds.
Add another function, test_double_matrix_exceptions(), which will catch this
exception and do something appropriate, like print an error message and continue
processing. Modify your main, by adding a call to this new function as shown
below. Ensure that generate_exception indexes a Matrix out of bounds to cause
this exception to be thrown. Add proper throw specifications to any function that
may throw this exception.
void generate_exception( Matrix < double &m )
{
// insert a for loop that cause the exception
}
void test_double_matrix_exceptions()
{
// PUT YOUR TRY/CATCH AROUND THE INSTRUCTIONS BELOW
cout << “Starting...\n”;
Matrix < double M(8,10);
fillMatrix( M );
cout << M;
generate_exception( M );
cout << “Done\n”;
}
int main()
{
for (int i=0; i<3; ++i)
{
test_int_matrix();
test_double_matrix();
test_double_matrix_exceptions();
}
return 0;
}
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