1. Computing Fundamentals with C++
Object-Oriented Programming and Design, 2nd Edition
Rick Mercer
Franklin, Beedle & Associates, 1999
ISBN
Presentation Copyright 1999, Franklin, Beedle & Associates
Students who purchase and instructors who adopt Computing Fundamentals with C++, Object-Oriented Programming and Design by Rick Mercer are welcome to use this presentation as long as this copyright notice remains intact.

2. Chapter 19 Doubly Subscripted Objects
Chapter Objectives
process tabular data
perform row-by-row and column-by-column processing of tabular data
declare primitive arrays with two or three subscripts
manipulate the data of a visibility research study using a doubly subscripted (one for rows, one for columns) object

3. 19.1 Matrix Data
Data is sometimes conveniently viewed as tabular--rows and columns
Week#
Student#
An Attendance Sheet
Code: 1 represents attendance, 0 indicates absence.

4. 19.1 A matrix class
a matrix object stores a collection of objects (of the same class)
a matrix object is a fixed size (but it can be 'resized')
Individual objects are referenced with two subscripts, one for the row and one for the column. Always start at 0
matrix is NOT a standard C++ class
It was written by the author

5. General form of a matrix object declaration
Must include matrix:
#include "matrix" // for class matrix
General form:
matrix < class > identifier ( rows , columns ) ;
Example:
// a matrix object with 10 rows and 15 columns
matrix<int> student(10, 15);
If you do not want to use matrix, declare like this
int student[10][15];

6. Referencing individual matrix elements
A reference to an individual element of matrix requires two subscripts (row and column):
matrix-name [ row ] [ column ]
Each subscript must be bracketed individually.
Examples
student[0][0] = 1;
student[9][14] = 0;

7. Errors may occur when referencing individual matrix elements
These expressions generate errors:
student[1] // require 2 subscripts
student[-1][0] // There is no row -1
student[1][15] // There is no column 15
student[2, 3] // An error made by Pascalites
If your subscript is out of range, a runtime error occurs. The program is terminated

8. Nested Looping (no matrix object)
Nested for loops are often used to process the data stored in a matrix
Consider a loop inside another
int outer, inner;
for(outer = 0; outer < 4; outer++) {
for(inner = 0; inner <= outer; inner++)
cout << inner << " "; }
cout << endl;
Output? ______ ?

9. Nested for loops to visit every element in a matrix object
#include "matrix" // for the matrix<Type> class
int main() {
matrix <int> t(4, 6); // 4 x 6 ints
int row, col;
for(row = 0; row < 4; row++)
{ // Initialize one row
for(col = 0; col < 6; col++)
{ // Reference each column in the row
t[row][col] = row * col; }
// continued on next slide

10. Display elements row by row
for(row = 0; row < 4; row++)
{ // Display one row
for(col = 0; col < 6; col++)
{ // Display each column of the row
cout << t[row][col] << " "; }
cout << endl;
return 0;
Output?______?

11. Active Learning
Write the code that displays the sum of each row of data. Answer in:
sumrows.cpp
Your output should look like this:
Sum of row #0 = 0
Sum of row #1 = 10
Sum of row #2 = 30
Sum of row #4 = 45

12. class quizData (with a matrix data member)
A quizData object to demonstrate matrix processing (the class definition)
class quizData {
public:
quizData(string filename); // constructor
void display() const; // accessor
void studentStats() const; // accessor
void quizStats() const; // accessor
double average() const; // accessor
private:
int lastStudent, lastQuiz;
matrix <double> quiz; };

13. quizData::quizData quizData::quizData(string fileName)
{ // Initialize quiz (assuming filename exists)
ifstream inFile(filename.c_str() );
int row, col;
// Input the size of the data
inFile >> lastStudent >> lastQuiz;
// Initialize a lastStudent by lastQuiz matrix
for(row = 0; row < lastStudent; row++) {
for(col = 0; col < lastQuiz; col++)
inFile >> quiz[row][col]; }
} // end constructor implementation

14. quizData::display void quizData::display() { int row = 0; int col = 0;
cout << "\nQuiz data:" << endl;
for(row = 0; row < lastStudent; row++)
for(col = 0; col < lastQuiz; col++)
cout.width(6);
cout << quiz[row][col]; }
cout << endl;
} // end quizData::display() implementation

15. quizData::studentStats
void quizData::studentStats()
{ // pre: lastQuiz > 1
// An example of row by row processing
double sum, lowest, average;
int row, col;
cout << endl;
cout << " Student Average" << endl;
cout << " ======= =======" << endl;
cout.setf(ios::fixed, ios::floatfield);
cout.setf(ios::showpoint);
cout.precision(1);
// continued on next slide

16. row by row processing
for(row = 0; row < lastStudent; row++) //outer loop {
// Assume the first quiz is the lowest
lowest = quiz[row][0];
// Assign sum the value of the first quiz
sum = lowest;
// Process the remaining quizzes (start at 1)
for(col = 1; col < lastQuiz; col++) // inner loop
sum += quiz[row][col];
if(quiz[row][col] < lowest)
lowest = quiz[row][col];
} // end inner loop

17. Average all but lowest quiz
// Drop the lowest quiz
sum = sum - lowest;
// Divide by 1 less because of dropped quiz
average = sum / (lastQuiz - 1);
cout.width(10);
cout << row;
cout.width(15);
cout << average << endl;
} // end outer loop
} // end quizData::studentStats

18. Primitive C arrays C++ has primitive arrays
with one, two, three, four,... subscripts
Examples:
string myFriends[100]; // store up to 100 strings
double x[10][5]; // store up to 150 numbers
This gives you row subscripts 0..9 and column subscripts 0..4
You do not get subscript range checking

19. Compare C arrays to matrix

20. More than 2 subscripts
C++ does not limit the number of subscripts that you can use
Arrays with three or more subscripts are sometimes used
The declaration follows the pattern of the doubly subscripted matrix
double q[4][12][7]
This would give 4 x 12 x 7 cube with subscripts 0..3, 0..1, and respectively