Chapter 1 PROGRAMMING PRINCIPLES
1,Introduction, Problems with large
programs
2.The Game of Life (a continuing
example)
3,Programming style
4,Coding,Testing,and Further
Refinement
5,Program Maintenance
6,Preview
(a) Software Engineering
(b) Problem Analysis
(c) Requirements
Specification
(d) Coding
7,Pointers and Pitfalls
8,References
Problems of Large Programs
1,The patchwork approach
2,Problem specification
3,Program organization
4,Data organization and data structures
5,Algorithm selection and analysis
6,Debugging
7,Testing and verification
8,Maintenance
1.1 Introduction
9,Highlights of C++
(a) Data abstraction
(b) Object-oriented design
(c) Reusable code
(d) Refinement,improvement,extension of C
Rules for the Game of Life
1,The neighbors of a given cell are the eight
cells
that touch it vertically,horizontally,or
diagonally,Every cell is either living or
dead.
2,A living cell stays alive in the next
generation if it has either 2 or 3 living
neighbors; it dies if it has 0,1,4,or more
1.2 The Game of life
3,A dead cell becomes alive in the next
generation if it has exactly three neighboring
cells,no more or fewer,that are already
alive,All other dead cells remain dead in the
next generation.
4,All births and deaths take place at exactly
the
same time,so that a dying cell can help to
give
birth to another,but cannot prevent the
death
of others by reducing overcrowding,nor
Life,Examples and Outline
Life,moribund
examples
Life,stability examples
next
generation
Life,alternation
examples
Set up a Life configuration as an initial
arrangement of living and dead cells.
While the user wants to see further
generations:
Update the configuration by applying the
rules of the Life game.
Print the current configuration.
C++ Classes,Objects,and Methods
A class collects data and the methods used to
access or change the data.
Such a collection of data and methods is
called an object belonging to the given class.
Every C++ class consists of members that
represent either variables (called data members)
or functions (called methods or member
functions),The member functions of a class are
normally used to access or alter the data
members.
Example,For the Life game,the class is
called Life,and configuration becomes a Life
object,We use three methods,initialize( ) will
set up the initial configuration of living and dead
cells; print( ) will print out the current
configuration; and update( ) will make all the
changes that occur in moving from one
generation to the next,
Clients,that is,user programs with access to
a particular class,can declare and manipulate
objects of that class.
The specifications of a method,function,or
program are statements of precisely what is
done,Preconditions state what is required
before; Postconditions state what has happened
when the method,function,or program has
finished.
Programming Precept
Include precise specifications
with every program,function,and method that
you write.
Information Hiding
By relying on its specifications,a client can
use a method without needing to know how the
data are actually stored or how the methods are
actually programmed,This important
programming strategy known as information
hiding.
Data members and methods available to a
client are called public; further private variables
and functions may be used in the
implementation of the class,but are not
available to a client.
Convention
Methods of a class are public.
Functions in a class are private.
Life,The Main Program
#include "utility.h"
#include "life.h"
void main( )
/* Pre,The user supplies an initial configuration
of living cells.
Post,The program prints a sequence of
pictures
showing the changes in the
configuration
of living cells according to the rules for
the game of Life.
Uses,The classLife and its methods
initialize(),
print(),and update(),
{ void instructions( ); Life configuration;
instructions( );
configuration.initialize( );
configuration.print( );
cout << "Continue viewing new
generations?\n ";
while (user_says_yes( ))
{ configuration.update( );
configuration.print( );
cout << "Continue viewing new
generations?\n";
}
}
Examples of Life Configurations
Examples of Life Configurations(continue)
1.3.1 names
Guidelines for Choosing Names
1.3 Programming
style
Programming Precept
Always name your classes,variables,and
functions
with the greatest care,and explain them
thoroughly.
1,Give special care to the choice of names for
classes,functions,constants,and all global
variables used in different parts of the program.
2,Keep the names simple for variables used
only
briefly and locally.
3,Use common prefixes or suffixes to associate
names of the same general category.
4,Avoid deliberate misspellings and
meaningless
5,Avoid choosing cute names whose meaning
has
little or nothing to do with the problem.
6,Avoid choosing names that are close to each
other
in spelling or otherwise easy to confuse.
7,Be careful in the use of the letter ‘l’ (small ell),
‘O’
(capital oh) and ‘0’ (zero).
Programming Precept
Keep your documentation concise but
descriptive.
1.3.2 Documentation and format
Documentation Guidelines
1,Place a prologue at the beginning of each
function
with
(a) Identification (programmer's name,date,
version).
(b) Statement of the purpose of the function and
method used.
(c) Changes the function makes and what data
it
uses.
2,When each variable,constant,or type is
declared,
explain what it is and how it is used.
3,Introduce each significant part of the program
with
a statement of purpose.
4,Indicate the end of each significant section.
5,Avoid comments that parrot what the code
does or
that are meaningless jargon.
7,The code itself should explain how the
program
works,The documentation should explain
why it
works and what it does.
8,Be sure to modify the documentation along
with
the program.
Programming Precept
The reading time for programs is much
more
than the writing time.
Make reading easy to do.
Top-down design and refinement:
Programming Precept
Don't lose sight of the forest for its
trees.
1.3,3 Refinement and
Modularity
Programming Precept
? Use classes to model the fundamental
concepts of the program.
? Each function should do only one task,
but do
it well.
? Each class or function should hide
something.
Division of work,
Categories of Data:
Input parameters
Output parameters
Inout parameters
Local variables
Global variables
Programming Precept
? Keep your connections simple,Avoid
global variables whenever possible.
? Never cause side effects if you can
avoid it.
If you must use global variables as
input,
document them thoroughly.
? Keep your input and output as separate
functions,so they can be changed
easily
int Life,,neighbor_count(int row,int col)
Pre,The Life object contains a
configuration,
and the coordinates row and col
define a
cell inside its hedge.
Post,The number of living neighbors of
Life Methods
void Life,,update( )
Pre,The Life object contains a
configuration.
Post,The Life object contains the next
generation of configuration.void instructions( )
Pre,None.
Post,Instructions for using the Life
program
are printed.
void Life,,initialize( )
Pre,None.
Post,The Life object contains a
configuration
specified by the user.
void Life,,print( )
Pre,The Life object contains a
configuration.
Post,The configuration is written for the
user.
1.4 Coding,Testing,
and Further Refinement
The three processes in the section
title go
hand-in-hand and must be done
together.
Yet it is important to keep them
separate in our thinking.since each
requires its own approach and method.
1.4.1 – 1.4.7
Coding
Coding is the process of writing an
algorithm in the correct syntax of a computer
language like C++;
Testing is the process of running the
program on sample data chosen to find errors
if they are present,For further refinement,
we turn s of the functions not yet written and
repeat these steps,
Definition of the Class Life
const int maxrow = 20,maxcol = 60;
class Life
{
public:
void initialize( );
void print( );
void update( );
private:
int grid[maxrow+2][maxcol+2];
int neighbor_count(int row,int col);
};
Size of grid
dimensions
allows for two extra
rows and columns
Size of grid
di ensions
al ows for two extra
rows and colu ns
Counting
Neighbors
int Life,,neighbor_count(int row,int col)
/* Pre,The Life object contains a configuration,and
the coordinates row and col define a cell inside
its hedge.
Post,The number of living neighbors of the specified
cell is returned,*/
{ int count=0;
for(int i=row-1; i<=row+1; i++)
for(int j=col-1; j<=col+1; j++)
count += grid[i][j];
count -= grid[row][col];
return count;
}
Increase the cou t
if neighbor is aliveReduce count,since cell is not
its own neighbor
Updating the Grid
void Life,,update( )
/* Pre,The Life object contains a configuration,
Post,The Life object contains the next generation of
configuration */
{ int row,col,new_grid[maxrow+2][maxcol+2];
for(row=1; row<=maxrow; row++)
for(col=1; col<=maxcol; col++)
switch (neighbor_count(row,col))
{ case 2:
new_grid[row][col]=grid[row][col];
break;
Status stays
the same
case 3:
new_grid[row][col]=1;
break;
default:
new_grid[row][col]=0;
}
for(row=1; row<=maxrow; row++)
for(col=1; col<=maxcol; col++)
grid[row][col] = new_grid[row][col];
}
Cell is now aliveCell is now dead
Instructions
void instructions( )
/* Pre,None.
Post,Instructions for using the Life program have
been printed,*/
{
cout<<"Welcome to Conway's game of Life.\n";
cout<<"This game uses a grid of size ";
cout<<maxrow<<" by "<<maxcol
cout<<" in which each\n";
cout << "cell can either be occupied by an
organism
or not." << endl;
cout << "The occupied cells change from
generation to generation\n";
cout << "according to how many neighboring cells
are alive.\n";
}
Output
void Life::print( )
/* Pre,The Life object contains a configuration.
Post,The configuration is written for the user,*/
{ int row,col;
cout<<"\nThe current Life configuration is:\n";
for(row = 1; row <= maxrow; row++)
{ for(col = 1; col <= maxcol; col++)
if(grid[row][col]==1) cout<<'*'; else cout<<' ';
cout<<endl;
}
}
Initialization
void Life::initialize( )
/* Pre,None.
Post,The Life object contains a configuration
specified by the user,*/
{ int row,col;
for(row=0; row<=maxrow+1; row++)
for(col=0; col<=maxcol+1; col++)
grid[row][col] = 0;
cout<<"List the coordinates for living cells.\n";
cout<<"Terminate the list with the the special pair”;
cout<< " -1 -1" << endl;
cin>>row>>col;
while(row!= -1||col!=-1)
{ if(row>=1 && row<=maxrow)
if(col>=1 && col<=maxcol) grid[row][col]=1;
else
cout<<"Column "<<col<<" is out of range.\n";
else
cout<<"Row "<<row<<" is out of range.\n";
cin>>row>>col;
}
}
.
Utility Package
We shall assemble a utility package that
contains various declarations and
functions that prove useful in a variety of
programs,even though these are not
related to each other as we might expect
if we put them in a class.
For example,we shall put declarations
to help with error processing in the
utility package.
Utility Package
Our first function for the utility
package
obtains a yes-no response from the
user:bool user_says_yes( )
Pre,None.
Post,Returns true if the user enters ?y? or
?Y?;
returns false if the user enters ?n? or
?N?;
otherwise requests new response
bool user_says_yes( )
{ char c;
bool initial_response = true;
do
{ if (initial_response) cout<<" (y,n)? " <<flush;
else cout << "Respond with either y or n,"<<flush;
do c=cin.get(); while(c == '\n' || c == ' ' || c=='\t');
initial_response=false;
}while(c!='y' && c!='Y' && c!='n' && c!='N');
return(c=='y' || c=='Y');
}
loop until
an appropriate input
is receivedacc pt a charignore whit space
Drivers
A driver for a function is an auxiliary
program whose purpose is to provide
the necessary input for the function,
call it,and evaluate the result.
void main( )
/* Pre,None.
Post,Verifies that the neighbor_ count( )
returns the correct values.
Uses,The class Life and its method
initialize() */
{ Life configuration;
configuration.initialize() ;
for(row=1; row<=maxrow; row++)
{ for(col=1; col<=maxcol; col++)
cout<<
configuration.neighbor_count(row,col)<<“,;
cout << endl ;
}
}
Driver for neighbor_count()
Sometimes two functions can used to check each
other,The easiest way,for example,to check the Life
Methods initialize( )and print( ) is to use a driver whose
action part is
configuration,initialize( ) ;
configuration,print( ) ;
Both methods can be tested by running this driver and
making sure that the configuration printed is
the same as that given as input.
Debugging and
Testing
Methods for debugging:
1,Structured walkthrough
2,Trace tools and
snapshots
3,Scaffolding
4,Static analyzer
Programming Precept
? The quality of test data is more
important
than its quantity.
? Program testing can be used to show
the
presence of bugs,but never their
absence.
Methods for program testing,
1,The black-box method:
(a) Easy values
(b) Typical,realistic values
(c) Extreme values
(d) Illegal values
2,The glass-box method,Trace all the
paths
through the program.
3,The ticking-box method,Don't do
anything — Just hope for the best!
Execution
Pathsswitch a{
case 1:
x = 3;
break;
case 2,
if(b==0)
x=2;
else x=4;
break;
case 3,
while(c>0)
process
(c);
break;
Execution
Paths
1.5.1 Program Evaluation
Programming Precept
For a large and important program,more
than half the work comes in the
maintenance phase,after it has been
completely debugged,tested,and put into
use.
1.5 Program Maintenance
1,Does the program solve the problem that is
requested,following the problem
specifications
exactly?
2,Does the program work correctly under all
conditions?
3,Does the program have a good user interface?
Can it receive input in forms convenient and
easy
for the user?Is its output clear,useful,and
attractively presented? Does the program
provide
alternatives and optional features to facilitate
4,Is the program logically and clearly
written,with
convenient classes and short functions as
appropriate to do logical tasks? Are the
data
structured into classes that accurately
reflect
the needs of the program?
5,Is the program well documented? Do the
names
accurately reflect the use and meaning of
variables,functions,types,and methods?
Are
6,Does the program make efficient use of time
and
of space? By changing the underlying
algorithm,
could the program's performance be improved?1.5.2-1.5.3 Programming Precept
? Be sure you understand your problem
completely,If you must change its terms,
explain exactly what you have done.
? Design the user interface with the greatest
care
possible,A program's success depends
greatly
? Do not optimize your code unless it is
necessary
to do so,Do not start to optimize code until it
is
complete and correct.
Most programs spend 90 percent of their
time
doing 10 percent of their instructions,Find this
10 percent,and concentrate your efforts for
efficiency there.
? Keep your algorithms as simple as you can.
When in doubt,choose the simple way.
1.6 Conclusion and
Preview1.6.1 Software Engineering
Software Engineering is the study and
practice of methods helpful for the
construction and maintenance of large
software system.
Software Life Cycle
1,Analyze the problem precisely and
completely,
Be sure to specify all necessary user
interface
with care.
2,Build a prototype and experiment with it
until all
specifications can be finalized.
3,Design the algorithm,using the tools of
data
structures and of other algorithms whose
function is already known.
requirements,Make sure that it meets the
specifications.
6,Code the algorithm into the appropriate
programming language.
7,Test and evaluate the program on carefully
chosen
test data.
8,Rene and repeat the foregoing steps as
needed for
additional functions until the software is
complete
and fully functional.
9,Optimize the code to improve performance,
but
1.6.2 Problem Analysis
1,What form will the input and output data
take?
How much data will there be?
2,Are there any special requirements for the
processing? What special occurrences will
require separate treatment?
3,Will these requirements change? How?
How fast
will the demands on the system grow?
4,What parts of the system are the most
5,How should erroneous data be treated?
What
other error processing is needed?
6,What kinds of people will use the software?
What kind of training will they have? What
kind
of user interface will be best?
7,How portable must the software be,to move
to
new kinds of equipment? With what other
software and hardware systems must the
project
be compatible?
1.6.3 Requirements Specification
1,Functional requirements for the system,what
it
will do and what commands will be available
to
the user.
2,Assumptions and limitations on the system,
what
hardware will be used for the system,what
form
the input must take,the maximum size of
input,
4,Documentation requirements,what kind of
explanatory material is required for what
kinds of
users.
The requirements specifications state
what the software will do,not how it will be
done.
1.6.4 Coding (Precepts on Coding)
Programming Precept
? Never code until the specifications are
precise and complete.
? Act in haste and repent at leisure,Program
in
haste and debug forever.
? Starting afresh is often easier than patching
an old
program.
? Always plan to build a prototype and throw it
1.7 Pointers and Pitfalls
1,To improve your program,review the logic,
Don't optimize code based on a poor
algorithm.
2,Never optimize a program until it is correct
and
working.
3,Don't optimize code unless it is absolutely
necessary.
4,Keep your functions short; rarely should any
5,Be sure your algorithm is correct before
starting
to code.
6,Verify the intricate parts of your algorithm.
7,Keep your logic simple.
8,Be sure you understand your problem
before you
decide how to solve it.
9,Be sure you understand the algorithmic
method
before you start to program.
11,The nouns that arise in describing a problem
suggest useful classes for its solution; the
verbs
suggest useful functions.
12,Include careful documentation (as
presented in
Section 1.3.2) with each function as you
write it.
13,Be careful to write down precise
preconditions
and postconditions for every function.
15,Every time a function is used,ask yourself
why
you know that its preconditions will be
satisfied.
16,Use stubs and drivers,black-box and glass-
box
testing to simplify debugging.
17,Use plenty of scaffolding to help localize
errors.
18,In programming with arrays,be wary of
index
20,Keep your documentation consistent with
your
code,and when reading a program make
sure
that you debug the code and not just the
comments.
21,Explain your program to somebody else,
Doing
so will help you understand it better
yourself.
1,Introduction, Problems with large
programs
2.The Game of Life (a continuing
example)
3,Programming style
4,Coding,Testing,and Further
Refinement
5,Program Maintenance
6,Preview
(a) Software Engineering
(b) Problem Analysis
(c) Requirements
Specification
(d) Coding
7,Pointers and Pitfalls
8,References
Problems of Large Programs
1,The patchwork approach
2,Problem specification
3,Program organization
4,Data organization and data structures
5,Algorithm selection and analysis
6,Debugging
7,Testing and verification
8,Maintenance
1.1 Introduction
9,Highlights of C++
(a) Data abstraction
(b) Object-oriented design
(c) Reusable code
(d) Refinement,improvement,extension of C
Rules for the Game of Life
1,The neighbors of a given cell are the eight
cells
that touch it vertically,horizontally,or
diagonally,Every cell is either living or
dead.
2,A living cell stays alive in the next
generation if it has either 2 or 3 living
neighbors; it dies if it has 0,1,4,or more
1.2 The Game of life
3,A dead cell becomes alive in the next
generation if it has exactly three neighboring
cells,no more or fewer,that are already
alive,All other dead cells remain dead in the
next generation.
4,All births and deaths take place at exactly
the
same time,so that a dying cell can help to
give
birth to another,but cannot prevent the
death
of others by reducing overcrowding,nor
Life,Examples and Outline
Life,moribund
examples
Life,stability examples
next
generation
Life,alternation
examples
Set up a Life configuration as an initial
arrangement of living and dead cells.
While the user wants to see further
generations:
Update the configuration by applying the
rules of the Life game.
Print the current configuration.
C++ Classes,Objects,and Methods
A class collects data and the methods used to
access or change the data.
Such a collection of data and methods is
called an object belonging to the given class.
Every C++ class consists of members that
represent either variables (called data members)
or functions (called methods or member
functions),The member functions of a class are
normally used to access or alter the data
members.
Example,For the Life game,the class is
called Life,and configuration becomes a Life
object,We use three methods,initialize( ) will
set up the initial configuration of living and dead
cells; print( ) will print out the current
configuration; and update( ) will make all the
changes that occur in moving from one
generation to the next,
Clients,that is,user programs with access to
a particular class,can declare and manipulate
objects of that class.
The specifications of a method,function,or
program are statements of precisely what is
done,Preconditions state what is required
before; Postconditions state what has happened
when the method,function,or program has
finished.
Programming Precept
Include precise specifications
with every program,function,and method that
you write.
Information Hiding
By relying on its specifications,a client can
use a method without needing to know how the
data are actually stored or how the methods are
actually programmed,This important
programming strategy known as information
hiding.
Data members and methods available to a
client are called public; further private variables
and functions may be used in the
implementation of the class,but are not
available to a client.
Convention
Methods of a class are public.
Functions in a class are private.
Life,The Main Program
#include "utility.h"
#include "life.h"
void main( )
/* Pre,The user supplies an initial configuration
of living cells.
Post,The program prints a sequence of
pictures
showing the changes in the
configuration
of living cells according to the rules for
the game of Life.
Uses,The classLife and its methods
initialize(),
print(),and update(),
{ void instructions( ); Life configuration;
instructions( );
configuration.initialize( );
configuration.print( );
cout << "Continue viewing new
generations?\n ";
while (user_says_yes( ))
{ configuration.update( );
configuration.print( );
cout << "Continue viewing new
generations?\n";
}
}
Examples of Life Configurations
Examples of Life Configurations(continue)
1.3.1 names
Guidelines for Choosing Names
1.3 Programming
style
Programming Precept
Always name your classes,variables,and
functions
with the greatest care,and explain them
thoroughly.
1,Give special care to the choice of names for
classes,functions,constants,and all global
variables used in different parts of the program.
2,Keep the names simple for variables used
only
briefly and locally.
3,Use common prefixes or suffixes to associate
names of the same general category.
4,Avoid deliberate misspellings and
meaningless
5,Avoid choosing cute names whose meaning
has
little or nothing to do with the problem.
6,Avoid choosing names that are close to each
other
in spelling or otherwise easy to confuse.
7,Be careful in the use of the letter ‘l’ (small ell),
‘O’
(capital oh) and ‘0’ (zero).
Programming Precept
Keep your documentation concise but
descriptive.
1.3.2 Documentation and format
Documentation Guidelines
1,Place a prologue at the beginning of each
function
with
(a) Identification (programmer's name,date,
version).
(b) Statement of the purpose of the function and
method used.
(c) Changes the function makes and what data
it
uses.
2,When each variable,constant,or type is
declared,
explain what it is and how it is used.
3,Introduce each significant part of the program
with
a statement of purpose.
4,Indicate the end of each significant section.
5,Avoid comments that parrot what the code
does or
that are meaningless jargon.
7,The code itself should explain how the
program
works,The documentation should explain
why it
works and what it does.
8,Be sure to modify the documentation along
with
the program.
Programming Precept
The reading time for programs is much
more
than the writing time.
Make reading easy to do.
Top-down design and refinement:
Programming Precept
Don't lose sight of the forest for its
trees.
1.3,3 Refinement and
Modularity
Programming Precept
? Use classes to model the fundamental
concepts of the program.
? Each function should do only one task,
but do
it well.
? Each class or function should hide
something.
Division of work,
Categories of Data:
Input parameters
Output parameters
Inout parameters
Local variables
Global variables
Programming Precept
? Keep your connections simple,Avoid
global variables whenever possible.
? Never cause side effects if you can
avoid it.
If you must use global variables as
input,
document them thoroughly.
? Keep your input and output as separate
functions,so they can be changed
easily
int Life,,neighbor_count(int row,int col)
Pre,The Life object contains a
configuration,
and the coordinates row and col
define a
cell inside its hedge.
Post,The number of living neighbors of
Life Methods
void Life,,update( )
Pre,The Life object contains a
configuration.
Post,The Life object contains the next
generation of configuration.void instructions( )
Pre,None.
Post,Instructions for using the Life
program
are printed.
void Life,,initialize( )
Pre,None.
Post,The Life object contains a
configuration
specified by the user.
void Life,,print( )
Pre,The Life object contains a
configuration.
Post,The configuration is written for the
user.
1.4 Coding,Testing,
and Further Refinement
The three processes in the section
title go
hand-in-hand and must be done
together.
Yet it is important to keep them
separate in our thinking.since each
requires its own approach and method.
1.4.1 – 1.4.7
Coding
Coding is the process of writing an
algorithm in the correct syntax of a computer
language like C++;
Testing is the process of running the
program on sample data chosen to find errors
if they are present,For further refinement,
we turn s of the functions not yet written and
repeat these steps,
Definition of the Class Life
const int maxrow = 20,maxcol = 60;
class Life
{
public:
void initialize( );
void print( );
void update( );
private:
int grid[maxrow+2][maxcol+2];
int neighbor_count(int row,int col);
};
Size of grid
dimensions
allows for two extra
rows and columns
Size of grid
di ensions
al ows for two extra
rows and colu ns
Counting
Neighbors
int Life,,neighbor_count(int row,int col)
/* Pre,The Life object contains a configuration,and
the coordinates row and col define a cell inside
its hedge.
Post,The number of living neighbors of the specified
cell is returned,*/
{ int count=0;
for(int i=row-1; i<=row+1; i++)
for(int j=col-1; j<=col+1; j++)
count += grid[i][j];
count -= grid[row][col];
return count;
}
Increase the cou t
if neighbor is aliveReduce count,since cell is not
its own neighbor
Updating the Grid
void Life,,update( )
/* Pre,The Life object contains a configuration,
Post,The Life object contains the next generation of
configuration */
{ int row,col,new_grid[maxrow+2][maxcol+2];
for(row=1; row<=maxrow; row++)
for(col=1; col<=maxcol; col++)
switch (neighbor_count(row,col))
{ case 2:
new_grid[row][col]=grid[row][col];
break;
Status stays
the same
case 3:
new_grid[row][col]=1;
break;
default:
new_grid[row][col]=0;
}
for(row=1; row<=maxrow; row++)
for(col=1; col<=maxcol; col++)
grid[row][col] = new_grid[row][col];
}
Cell is now aliveCell is now dead
Instructions
void instructions( )
/* Pre,None.
Post,Instructions for using the Life program have
been printed,*/
{
cout<<"Welcome to Conway's game of Life.\n";
cout<<"This game uses a grid of size ";
cout<<maxrow<<" by "<<maxcol
cout<<" in which each\n";
cout << "cell can either be occupied by an
organism
or not." << endl;
cout << "The occupied cells change from
generation to generation\n";
cout << "according to how many neighboring cells
are alive.\n";
}
Output
void Life::print( )
/* Pre,The Life object contains a configuration.
Post,The configuration is written for the user,*/
{ int row,col;
cout<<"\nThe current Life configuration is:\n";
for(row = 1; row <= maxrow; row++)
{ for(col = 1; col <= maxcol; col++)
if(grid[row][col]==1) cout<<'*'; else cout<<' ';
cout<<endl;
}
}
Initialization
void Life::initialize( )
/* Pre,None.
Post,The Life object contains a configuration
specified by the user,*/
{ int row,col;
for(row=0; row<=maxrow+1; row++)
for(col=0; col<=maxcol+1; col++)
grid[row][col] = 0;
cout<<"List the coordinates for living cells.\n";
cout<<"Terminate the list with the the special pair”;
cout<< " -1 -1" << endl;
cin>>row>>col;
while(row!= -1||col!=-1)
{ if(row>=1 && row<=maxrow)
if(col>=1 && col<=maxcol) grid[row][col]=1;
else
cout<<"Column "<<col<<" is out of range.\n";
else
cout<<"Row "<<row<<" is out of range.\n";
cin>>row>>col;
}
}
.
Utility Package
We shall assemble a utility package that
contains various declarations and
functions that prove useful in a variety of
programs,even though these are not
related to each other as we might expect
if we put them in a class.
For example,we shall put declarations
to help with error processing in the
utility package.
Utility Package
Our first function for the utility
package
obtains a yes-no response from the
user:bool user_says_yes( )
Pre,None.
Post,Returns true if the user enters ?y? or
?Y?;
returns false if the user enters ?n? or
?N?;
otherwise requests new response
bool user_says_yes( )
{ char c;
bool initial_response = true;
do
{ if (initial_response) cout<<" (y,n)? " <<flush;
else cout << "Respond with either y or n,"<<flush;
do c=cin.get(); while(c == '\n' || c == ' ' || c=='\t');
initial_response=false;
}while(c!='y' && c!='Y' && c!='n' && c!='N');
return(c=='y' || c=='Y');
}
loop until
an appropriate input
is receivedacc pt a charignore whit space
Drivers
A driver for a function is an auxiliary
program whose purpose is to provide
the necessary input for the function,
call it,and evaluate the result.
void main( )
/* Pre,None.
Post,Verifies that the neighbor_ count( )
returns the correct values.
Uses,The class Life and its method
initialize() */
{ Life configuration;
configuration.initialize() ;
for(row=1; row<=maxrow; row++)
{ for(col=1; col<=maxcol; col++)
cout<<
configuration.neighbor_count(row,col)<<“,;
cout << endl ;
}
}
Driver for neighbor_count()
Sometimes two functions can used to check each
other,The easiest way,for example,to check the Life
Methods initialize( )and print( ) is to use a driver whose
action part is
configuration,initialize( ) ;
configuration,print( ) ;
Both methods can be tested by running this driver and
making sure that the configuration printed is
the same as that given as input.
Debugging and
Testing
Methods for debugging:
1,Structured walkthrough
2,Trace tools and
snapshots
3,Scaffolding
4,Static analyzer
Programming Precept
? The quality of test data is more
important
than its quantity.
? Program testing can be used to show
the
presence of bugs,but never their
absence.
Methods for program testing,
1,The black-box method:
(a) Easy values
(b) Typical,realistic values
(c) Extreme values
(d) Illegal values
2,The glass-box method,Trace all the
paths
through the program.
3,The ticking-box method,Don't do
anything — Just hope for the best!
Execution
Pathsswitch a{
case 1:
x = 3;
break;
case 2,
if(b==0)
x=2;
else x=4;
break;
case 3,
while(c>0)
process
(c);
break;
Execution
Paths
1.5.1 Program Evaluation
Programming Precept
For a large and important program,more
than half the work comes in the
maintenance phase,after it has been
completely debugged,tested,and put into
use.
1.5 Program Maintenance
1,Does the program solve the problem that is
requested,following the problem
specifications
exactly?
2,Does the program work correctly under all
conditions?
3,Does the program have a good user interface?
Can it receive input in forms convenient and
easy
for the user?Is its output clear,useful,and
attractively presented? Does the program
provide
alternatives and optional features to facilitate
4,Is the program logically and clearly
written,with
convenient classes and short functions as
appropriate to do logical tasks? Are the
data
structured into classes that accurately
reflect
the needs of the program?
5,Is the program well documented? Do the
names
accurately reflect the use and meaning of
variables,functions,types,and methods?
Are
6,Does the program make efficient use of time
and
of space? By changing the underlying
algorithm,
could the program's performance be improved?1.5.2-1.5.3 Programming Precept
? Be sure you understand your problem
completely,If you must change its terms,
explain exactly what you have done.
? Design the user interface with the greatest
care
possible,A program's success depends
greatly
? Do not optimize your code unless it is
necessary
to do so,Do not start to optimize code until it
is
complete and correct.
Most programs spend 90 percent of their
time
doing 10 percent of their instructions,Find this
10 percent,and concentrate your efforts for
efficiency there.
? Keep your algorithms as simple as you can.
When in doubt,choose the simple way.
1.6 Conclusion and
Preview1.6.1 Software Engineering
Software Engineering is the study and
practice of methods helpful for the
construction and maintenance of large
software system.
Software Life Cycle
1,Analyze the problem precisely and
completely,
Be sure to specify all necessary user
interface
with care.
2,Build a prototype and experiment with it
until all
specifications can be finalized.
3,Design the algorithm,using the tools of
data
structures and of other algorithms whose
function is already known.
requirements,Make sure that it meets the
specifications.
6,Code the algorithm into the appropriate
programming language.
7,Test and evaluate the program on carefully
chosen
test data.
8,Rene and repeat the foregoing steps as
needed for
additional functions until the software is
complete
and fully functional.
9,Optimize the code to improve performance,
but
1.6.2 Problem Analysis
1,What form will the input and output data
take?
How much data will there be?
2,Are there any special requirements for the
processing? What special occurrences will
require separate treatment?
3,Will these requirements change? How?
How fast
will the demands on the system grow?
4,What parts of the system are the most
5,How should erroneous data be treated?
What
other error processing is needed?
6,What kinds of people will use the software?
What kind of training will they have? What
kind
of user interface will be best?
7,How portable must the software be,to move
to
new kinds of equipment? With what other
software and hardware systems must the
project
be compatible?
1.6.3 Requirements Specification
1,Functional requirements for the system,what
it
will do and what commands will be available
to
the user.
2,Assumptions and limitations on the system,
what
hardware will be used for the system,what
form
the input must take,the maximum size of
input,
4,Documentation requirements,what kind of
explanatory material is required for what
kinds of
users.
The requirements specifications state
what the software will do,not how it will be
done.
1.6.4 Coding (Precepts on Coding)
Programming Precept
? Never code until the specifications are
precise and complete.
? Act in haste and repent at leisure,Program
in
haste and debug forever.
? Starting afresh is often easier than patching
an old
program.
? Always plan to build a prototype and throw it
1.7 Pointers and Pitfalls
1,To improve your program,review the logic,
Don't optimize code based on a poor
algorithm.
2,Never optimize a program until it is correct
and
working.
3,Don't optimize code unless it is absolutely
necessary.
4,Keep your functions short; rarely should any
5,Be sure your algorithm is correct before
starting
to code.
6,Verify the intricate parts of your algorithm.
7,Keep your logic simple.
8,Be sure you understand your problem
before you
decide how to solve it.
9,Be sure you understand the algorithmic
method
before you start to program.
11,The nouns that arise in describing a problem
suggest useful classes for its solution; the
verbs
suggest useful functions.
12,Include careful documentation (as
presented in
Section 1.3.2) with each function as you
write it.
13,Be careful to write down precise
preconditions
and postconditions for every function.
15,Every time a function is used,ask yourself
why
you know that its preconditions will be
satisfied.
16,Use stubs and drivers,black-box and glass-
box
testing to simplify debugging.
17,Use plenty of scaffolding to help localize
errors.
18,In programming with arrays,be wary of
index
20,Keep your documentation consistent with
your
code,and when reading a program make
sure
that you debug the code and not just the
comments.
21,Explain your program to somebody else,
Doing
so will help you understand it better
yourself.
