1
Program Input and the
Software Design Process
2
Chapter 4 Topics
Input Statements to Read Values for a Program
using >>,and functions get,ignore,getline
Prompting for Interactive Input/Output
Noninteractive Input/Output
Using Data Files for Input and Output
Input Failure
Software Design Methodologies
Object-Oriented Design Principles
Functional Decomposition Methodology
3
No I/O is built into C++
a library provides input stream and output
stream
Keyboard Screenexecuting
program
istream ostream
4
Keyboard and Screen I/O
#include <iostream>
cin
(of type istream)
cout
(of type ostream)
Keyboard Screenexecutingprogram
input data output data
5
<iostream> is header file
The header file iostream contains the
definition of two data types:istream and
ostream
for a library that defines 3 objects
an istream object named cin (keyboard)
an ostream object named cout (screen)
an ostream object named cerr (screen)
6
Giving a Value to a Variable
In your program you can assign (give) a value to the
variable by using the assignment operator =
ageOfDog = 12;
or by another method,such as
cout <<,How old is your dog?”;
cin >> ageOfDog;
7
Extraction Operator ( >> )
variable cin is predefined to denote an input stream
from the standard input device ( the keyboard )
the extraction operator >> called,get from” takes
2 operands,The left operand is a stream
expression,such as cin--the right operand is a
variable of simple type.
operator >> attempts to extract the next item from
the input stream and store its value in the right
operand variable
8
Extraction Operator >>(cont.)
,skips over”
(actually reads but does not store
anywhere)
leading white space characters
as it reads your data from the input
stream (either keyboard or disk file)
9
Extraction Operator(cont.)
>> is a binary operator
>> is called the input or extraction operator
>> is left associative
EXPRESSION HAS VALUE
cin >> age cin
STATEMENT
cin >> age >> weight ;
10
SYNTAX
These examples yield the same result.
cin >> length ;
cin >> width ;
cin >> length >> width ;
Input Statements
cin >> Variable >> Variable,,,;
11
Extraction operator >>(cont.)
When using the extraction operator ( >> ) to
read input characters into a string variable,
the >> operator skips any leading whitespace
characters such as blanks and newlines
it then reads successive characters into the
string,and stops at the first trailing whitespace
character (which is not consumed,but
remains waiting in the input stream)
12
The Reading Marker and the
Newline Character
reading marker
newline (end-of-line )
The newline character is created by
hitting Enter or Return at the keyboard,
or by using the manipulator endl or,\n”
in a program.
13
char first ;
char middle ;
char last ;
cin >> first ;
cin >> middle ;
cin >> last ;
NOTE,A file reading marker is left pointing to the
newline character after the?C? in the input stream.
first middle last
Example 1:At keyboard you type:
A[space]B[space]C[Enter]
first middle last
‘ A? ‘ B? ‘ C?
14
Example 2:At keyboard you type:
[space]25[space]J[space]2[Enter]
int age ;
char initial ;
float bill ;
cin >> age ;
cin >> initial ;
cin >> bill ;
NOTE,A file reading marker is left pointing to the
newline character after the 2 in the input
stream.
age initial bill
age initial bill
25 ‘ J? 2.0
15
STATEMENTS CONTENTS MARKER
POSITION
int i ; 25 A\n
char ch ; 16.9\n
float x ;
cin >> i ; 25 A\n
16.9\n
cin >> ch ; 25 A\n
16.9\n
cin >> x ; 25 A\n
16.9\n
Example 3
i ch x
25
25 ‘ A?
i ch x
i ch x
i ch x
16.925 ‘ A?
NOTE,shows the location of the file reading marker
16
The get( ) function can be used to
read a single character,
It obtains the very next character from
the input stream without skipping any
leading whitespace characters.
Another Way to Read char Data
17
char first ;
char middle ;
char last ;
cin.get ( first ) ;
cin.get ( middle ) ;
cin.get ( last ) ;
NOTE,The file reading marker is left pointing to the
space after the?B? in the input stream.
first middle last
An Example Using cin.get( )
At keyboard you type:
A[space]B[space]C[Enter]
first middle last
‘ A? ‘ ’ ‘ B?
18
Use function ignore( )
to skip characters
The ignore( ) function is used to skip (read and
discard) characters in the input stream,The call
cin.ignore ( howMany,whatChar ) ;
will skip over up to howMany characters or until
whatChar has been read,whichever comes first,
19
An Example Using cin.ignore( )
a b c
a b c
a b c
a b c
957 34
957 34 128
957 34
NOTE,shows the location of the file reading marker
STATEMENTS CONTENTS MARKER
POSITION
int a ; 957 34 1235\n
int b ; 128 96\n
int c ;
cin >> a >> b ; 957 34 1235\n
128 96\n
cin.ignore(100,?\n?) ; 957 34 1235\n
128 96\n
cin >> c ; 957 34 1235\n
128 96\n
20
Another Example Using cin.ignore( )
i ch
957 34
957 34
957 34
i ch
i ch
i ch
16 ‘ A?
‘ A?
‘ A?
NOTE,shows the location of the file reading marker
STATEMENTS CONTENTS MARKER
POSITION
int i ; A 22 B 16 C 19\n
char ch ;
cin >> ch ; A 22 B 16 C 19\n
cin.ignore(100,?B?) ; A 22 B 16 C 19\n
cin >> i ; A 22 B 16 C 19\n
21
EXAMPLE
string message ;
cin >> message ;
cout << message ;
HOWEVER,,,
String Input in C++
Input of a string is possible using the
extraction operator >>.
22
String Input Using >>
string firstName ;
string lastName ;
cin >> firstName >> lastName ;
Suppose input stream looks like this:
Joe Hernandez 23
WHAT ARE THE STRING VALUES?
23
Results Using >>
string firstName ;
string lastName ;
cin >> firstName >> lastName ;
RESULT
firstName lastName
,Hernandez”Joe
24
getline( ) Function
Because the extraction operator stops reading at
the first trailing whitespace,>> cannot be used
to input a string with blanks in it
use getline function with 2 arguments to
overcome this obstacle
First argument is an input stream variable,and
second argument is a string variable
EXAMPLE
string message ;
getline (cin,message ) ;
25
getline(inFileStream,str)
getline does not skip leading whitespace
characters such as blanks and newlines
getline reads successive characters
(including blanks) into the string,and
stops when it reaches the newline
character?\n?
the newline is consumed by get,but is not
stored into the string variable
26
String Input Using getline
string firstName ;
string lastName ;
getline (cin,firstName );
getline (cin,lastName );
Suppose input stream looks like this:
Joe Hernandez 23
WHAT ARE THE STRING VALUES?
27
Results Using getline
firstName lastName
string firstName ;
string lastName ;
getline (cin,firstName );
getline (cin,lastName );
,Joe Hernandez 23”
28
Interactive I/O
in an interactive program the user enters
information while the program is executing
before the user enters data,a prompt should be
provided to explain what type of information
should be entered
after the user enters data,the value of the data
should be printed out for verification,This is
called echo printing
that way,the user will have the opportunity to
check for erroneous data
29
Prompting for Interactive I/O
cout <<,Enter part number,,<< endl ; // prompt
cin >> partNumber ;
cout <<,Enter quantity ordered,,<< endl ;
cin >> quantity ;
cout <<,Enter unit price,,<< endl ;
cin >> unitPrice ;
totalPrice = quantity * unitPrice ; // calculate
cout <<,Part #,<< partNumber << endl ; // echo
cout <<,Quantity:,<< quantity << endl ;
cout <<,Unit Cost,$,<< setprecision(2)
<< unitPrice << endl ;
cout <<,Total Cost,$,<< totalPrice << endl ;
30
Noninteractive Input/Output
Many programs are written using noninteractive I/O
Example,batch processing
In batch processing,the user and the computer do not
Interact while the program running.The method is most
effective when a program is going to input or output large
amounts of data.
31
Diskette Files for I/O
your variable
(of type ifstream)
your variable
(of type ofstream)
disk file
“A:\myInfile.dat”
disk file
“A:\myOut.dat”
executing
program
input data output data
#include <fstream>
32
To Use Disk I/O,you must
use #include <fstream>
choose valid identifiers for your filestreams
and declare them
open the files and associate them with disk
names
use your filestream identifiers in your I/O
statements (using >> and <<,manipulators,
get,ignore)
close the files
33
Statements for Using Disk I/O
#include <fstream>
ifstream myInfile; // declarations
ofstream myOutfile;
myInfile.open(“A:\\myIn.dat”); // open files
myOutfile.open(“A:\\myOut.dat”);
myInfile.close( ); // close files
myOutfile.close( );
34
What does opening a file do?
associates the C++ identifier for your file with
the physical (disk) name for the file
if the input file does not exist on disk,open is
not successful
if the output file does not exist on disk,a new
file with that name is created
if the output file already exists,it is erased
places a file reading marker at the very
beginning of the file,pointing to the first
character in it
35
Map Measurement Case Study
You want a program to determine
walking distances between 4 sights in the
city,Your city map legend says one inch
on the map equals 1/4 mile in the city,
Read from a file the 4 measured
distances between sights on the map and
the map scale,
Output to a file the rounded (to the
nearest tenth) walking distances between
the 4 sights.
36
// ***************************************************
// Walk program using file I/O
// This program computes the mileage (rounded to nearest
// tenth of mile) for each of 4 distances,using input
// map measurements and map scale.
// ***************************************************
#include <iostream> // for cout,endl
#include <iomanip> // for setprecision
#include <fstream> // for file I/O
using namespace std;
float RoundToNearestTenth( float ); // declare function
An Example Program
Using File I/O
37
int main( )
{
float distance1; // First map distance
float distance2; // Second map distance
float distance3; // Third map distance
float distance4; // Fourth map distance
float scale; // Map scale (miles/inch)
float totMiles; // Total of rounded miles
float miles; // One rounded mileage
ifstream inFile; // First map distance
ofstream outFile; // Second map distance
outFile << fixed << showpoint // output file format
<< setprecision(1);
// Open the files
inFile.open(“walk.dat”);
outFile.open(“results.dat”);
38
// Get data from file
inFile >> distance1 >> distance2 >> distance3
>> distance4 >> scale;
totMiles = 0.0; // Initialize total miles
// Compute miles for each distance on map
miles = RoundToNearestTenth( distance1 * scale );
outFile << distance1 <<,inches on map is,
<< miles <<,miles in city.” << endl;
totMiles = totMiles + miles;
39
miles = RoundToNearestTenth( distance2 * scale );
outFile << distance2 <<,inches on map is,
<< miles <<,miles in city.” << endl;
totMiles = totMiles + miles;
miles = RoundToNearestTenth( distance3 * scale );
outFile << distance3 <<,inches on map is,
<< miles <<,miles in city.” << endl;
totMiles = totMiles + miles;
miles = RoundToNearestTenth( distance4 * scale );
outFile << distance4 <<,inches on map is,
<< miles <<,miles in city.” << endl;
totMiles = totMiles + miles;
40
// Write total miles to output file
outFile << endl <<,Total walking mileage is,
<< totMiles <<,miles.” << endl;
return 0 ; // Successful completion
}
// ***************************************************
float RoundToNearestTenth ( /* in */ float floatValue)
// Function returns floatValue rounded to nearest tenth.
{
return float(int(floatValue * 10.0 + 0.5)) / 10.0;
}
41
Run-Time Input of File Names
#include <string> // contains conversion function c_str
ifstream inFile;
string fileName;
cout <<,Enter input file name,,<< endl ; // prompt
cin >> fileName ;
// convert string fileName to a C string type
inFile.open( fileName.c_str( ) );
42
Input Failure
when a stream enters the fail state,further I/O
operations using that stream have no effect at
all,But the computer does not automatically
halt the program or give any error message
possible reasons for entering fail state include,
invalid input data (often the wrong type)
opening an input file that doesn’t exist
opening an output file on a diskette that is
already full or is write-protected
43
Software Design Methodologies
We describe two important design methodologies,
Object-oriented design
Functional decomposition
44
What is an object?
OBJECT
Operations
Data
set of functions
internal state
45
An object contains data
and operations
Private data:
accoutNumber
balance
OpenAccount
WriteCheck
MakeDeposit
IsOverdrawn
GetBalance
checkingAccount
46
Object-Oriented Design
A technique for developing a program in which
the solution is expressed in terms of objects --
self- contained entities composed of data and
operations on that data.
Private data
and function
<<
setf
.
.
.
Private data
and function
>>
get
.
.
.
ignore
cin cout
setw
47
More about OOD
languages supporting OOD include,C++,Java,
Smalltalk,Eiffel,CLOS,and Object-Pascal
a class is a programmer-defined data type and
objects are variables of that type
in C++,cin is an object of a data type (class) named
istream,and cout is an object of a class ostream,
Header files iostream and fstream contain
definitions of stream classes
a class generally contains private data and public
operations (called member functions)
48
Object-Oriented Design (OOD)
FOCUS is on entities called objects and operations on
those objects,all bundled together.
BEGINS by identifying the major objects in the problem,
and choosing appropriate operations on those objects,
UNITS are objects,Programs are collections of objects
that communicate with each other.
DATA plays a leading role,Algorithms are used to
implement operations on the objects and to enable
interaction of objects with each other.
49
Why use OOD with large
software projects?
objects within a program often model real-life
objects in the problem to be solved
many libraries of pre-written classes and objects
are available as-is for re-use in various programs
the OOD concept of inheritance allows the
customization of an existing class to meet
particular needs without having to inspect and
modify the source code for that class--this can
reduce the time and effort needed to design,
implement,and maintain large systems
50
Functional Decomposition
A technique for developing a program in
which the problem is divided into more
easily handled subproblems,the solutions
of which create a solution to the overall
problem.
In functional decomposition,we work from
the abstract (a list of the major steps in our
solution) to the particular (algorithmic
steps that can be translated directly into
code in C++ or another language),
51
Functional Decomposition
FOCUS is on actions and algorithms.
BEGINS by breaking the solution into a series of major
steps,This process continues until each subproblem
cannot be divided further or has an obvious solution,
UNITS are modules representing algorithms,A module
is a collection of concrete and abstract steps that
solves a subproblem,A module structure chart
(hierarchical solution tree) is often created,
DATA plays a secondary role in support of actions to be
performed.
52
Compute
Mileages
Write
Total Miles
Module Structure Chart
Main
Get Data
Round To
Nearest Tenth
Initialize
Total MilesOpen Files
53
A Perspective on Design
Functional decomposition and OOD are
not separate,disjoint techniques.
54
Two Programming
Methodologies
Functional Object-Oriented
Decomposition Design
FUNCTION
FUNCTION
FUNCTION
OBJECT
Operations
Data
OBJECT
Operations
Data
OBJECT
Operations
Data
55
Company Payroll Case Study
A small company needs an interactive
program to figure its weekly payroll,
The payroll clerk will input data for
each employee,Each employee?s
wages and data should be saved in a
secondary file,
Display the total wages for the week
on the screen.
56
Algorithm for Company Payroll
Program
Initialize total company payroll to 0.0
Repeat this process for each employee
1,Get the employee’s ID empNum
2,Get the employee’s hourly payRate
3,Get the hours worked this week
4,Calculate this week’s wages
5,Add wages to total company payroll
6,Write empNum,payRate,hours,wages to file
Write total company payroll on screen.
57
// ***************************************************
// Payroll program
// This program computes each employee’s wages and
// the total company payroll
// ***************************************************
#include <iostream> // for keyboard/screen I/O
#include <fstream> // for file I/O
using namespace std;
void CalcPay ( float,float,float& ) ;
const float MAX_HOURS = 40.0; // Maximum normal hours
const float OVERTIME = 1.5; // Overtime pay factor
Company Payroll Program
58
C++ Code Continued
int main( )
{
float payRate; // Employee’s pay rate
float hours; // Hours worked
float wages; // Wages earned
float total; // Total company payroll
int empNum; // Employee ID number
ofstream payFile; // Company payroll file
payFile.open(,payfile.dat” ); // Open file
total = 0.0; // Initialize total
59
cout <<,Enter employee number:,; // Prompt
cin >> empNum; // Read ID number
while ( empNum != 0 ) // While not done
{
cout <<,Enter pay rate:,;
cin >> payRate ; // Read pay rate
cout <<,Enter hours worked:,;
cin >> hours ; // and hours worked
CalcPay(payRate,hours,wages); // Compute wages
total = total + wages; // Add to total
payFile << empNum << payRate
<< hours << wages << endl;
cout <<,Enter employee number:,;
cin >> empNum; // Read ID number
}
60
cout <<,Total payroll is,
<< total << endl;
return 0 ; // Successful completion
}
// ***************************************************
void CalcPay ( /* in */ float payRate,
/* in */ float hours,
/* out */ float& wages )
// CalcPay computes wages from the employee’s pay rate
// and the hours worked,taking overtime into account
{
if ( hours > MAX_HOURS )
wages = (MAX_HOURS * payRate ) +
(hours - MAX_HOURS) * payRate * OVER_TIME;
else
wages = hours * payRate;
}
Program Input and the
Software Design Process
2
Chapter 4 Topics
Input Statements to Read Values for a Program
using >>,and functions get,ignore,getline
Prompting for Interactive Input/Output
Noninteractive Input/Output
Using Data Files for Input and Output
Input Failure
Software Design Methodologies
Object-Oriented Design Principles
Functional Decomposition Methodology
3
No I/O is built into C++
a library provides input stream and output
stream
Keyboard Screenexecuting
program
istream ostream
4
Keyboard and Screen I/O
#include <iostream>
cin
(of type istream)
cout
(of type ostream)
Keyboard Screenexecutingprogram
input data output data
5
<iostream> is header file
The header file iostream contains the
definition of two data types:istream and
ostream
for a library that defines 3 objects
an istream object named cin (keyboard)
an ostream object named cout (screen)
an ostream object named cerr (screen)
6
Giving a Value to a Variable
In your program you can assign (give) a value to the
variable by using the assignment operator =
ageOfDog = 12;
or by another method,such as
cout <<,How old is your dog?”;
cin >> ageOfDog;
7
Extraction Operator ( >> )
variable cin is predefined to denote an input stream
from the standard input device ( the keyboard )
the extraction operator >> called,get from” takes
2 operands,The left operand is a stream
expression,such as cin--the right operand is a
variable of simple type.
operator >> attempts to extract the next item from
the input stream and store its value in the right
operand variable
8
Extraction Operator >>(cont.)
,skips over”
(actually reads but does not store
anywhere)
leading white space characters
as it reads your data from the input
stream (either keyboard or disk file)
9
Extraction Operator(cont.)
>> is a binary operator
>> is called the input or extraction operator
>> is left associative
EXPRESSION HAS VALUE
cin >> age cin
STATEMENT
cin >> age >> weight ;
10
SYNTAX
These examples yield the same result.
cin >> length ;
cin >> width ;
cin >> length >> width ;
Input Statements
cin >> Variable >> Variable,,,;
11
Extraction operator >>(cont.)
When using the extraction operator ( >> ) to
read input characters into a string variable,
the >> operator skips any leading whitespace
characters such as blanks and newlines
it then reads successive characters into the
string,and stops at the first trailing whitespace
character (which is not consumed,but
remains waiting in the input stream)
12
The Reading Marker and the
Newline Character
reading marker
newline (end-of-line )
The newline character is created by
hitting Enter or Return at the keyboard,
or by using the manipulator endl or,\n”
in a program.
13
char first ;
char middle ;
char last ;
cin >> first ;
cin >> middle ;
cin >> last ;
NOTE,A file reading marker is left pointing to the
newline character after the?C? in the input stream.
first middle last
Example 1:At keyboard you type:
A[space]B[space]C[Enter]
first middle last
‘ A? ‘ B? ‘ C?
14
Example 2:At keyboard you type:
[space]25[space]J[space]2[Enter]
int age ;
char initial ;
float bill ;
cin >> age ;
cin >> initial ;
cin >> bill ;
NOTE,A file reading marker is left pointing to the
newline character after the 2 in the input
stream.
age initial bill
age initial bill
25 ‘ J? 2.0
15
STATEMENTS CONTENTS MARKER
POSITION
int i ; 25 A\n
char ch ; 16.9\n
float x ;
cin >> i ; 25 A\n
16.9\n
cin >> ch ; 25 A\n
16.9\n
cin >> x ; 25 A\n
16.9\n
Example 3
i ch x
25
25 ‘ A?
i ch x
i ch x
i ch x
16.925 ‘ A?
NOTE,shows the location of the file reading marker
16
The get( ) function can be used to
read a single character,
It obtains the very next character from
the input stream without skipping any
leading whitespace characters.
Another Way to Read char Data
17
char first ;
char middle ;
char last ;
cin.get ( first ) ;
cin.get ( middle ) ;
cin.get ( last ) ;
NOTE,The file reading marker is left pointing to the
space after the?B? in the input stream.
first middle last
An Example Using cin.get( )
At keyboard you type:
A[space]B[space]C[Enter]
first middle last
‘ A? ‘ ’ ‘ B?
18
Use function ignore( )
to skip characters
The ignore( ) function is used to skip (read and
discard) characters in the input stream,The call
cin.ignore ( howMany,whatChar ) ;
will skip over up to howMany characters or until
whatChar has been read,whichever comes first,
19
An Example Using cin.ignore( )
a b c
a b c
a b c
a b c
957 34
957 34 128
957 34
NOTE,shows the location of the file reading marker
STATEMENTS CONTENTS MARKER
POSITION
int a ; 957 34 1235\n
int b ; 128 96\n
int c ;
cin >> a >> b ; 957 34 1235\n
128 96\n
cin.ignore(100,?\n?) ; 957 34 1235\n
128 96\n
cin >> c ; 957 34 1235\n
128 96\n
20
Another Example Using cin.ignore( )
i ch
957 34
957 34
957 34
i ch
i ch
i ch
16 ‘ A?
‘ A?
‘ A?
NOTE,shows the location of the file reading marker
STATEMENTS CONTENTS MARKER
POSITION
int i ; A 22 B 16 C 19\n
char ch ;
cin >> ch ; A 22 B 16 C 19\n
cin.ignore(100,?B?) ; A 22 B 16 C 19\n
cin >> i ; A 22 B 16 C 19\n
21
EXAMPLE
string message ;
cin >> message ;
cout << message ;
HOWEVER,,,
String Input in C++
Input of a string is possible using the
extraction operator >>.
22
String Input Using >>
string firstName ;
string lastName ;
cin >> firstName >> lastName ;
Suppose input stream looks like this:
Joe Hernandez 23
WHAT ARE THE STRING VALUES?
23
Results Using >>
string firstName ;
string lastName ;
cin >> firstName >> lastName ;
RESULT
firstName lastName
,Hernandez”Joe
24
getline( ) Function
Because the extraction operator stops reading at
the first trailing whitespace,>> cannot be used
to input a string with blanks in it
use getline function with 2 arguments to
overcome this obstacle
First argument is an input stream variable,and
second argument is a string variable
EXAMPLE
string message ;
getline (cin,message ) ;
25
getline(inFileStream,str)
getline does not skip leading whitespace
characters such as blanks and newlines
getline reads successive characters
(including blanks) into the string,and
stops when it reaches the newline
character?\n?
the newline is consumed by get,but is not
stored into the string variable
26
String Input Using getline
string firstName ;
string lastName ;
getline (cin,firstName );
getline (cin,lastName );
Suppose input stream looks like this:
Joe Hernandez 23
WHAT ARE THE STRING VALUES?
27
Results Using getline
firstName lastName
string firstName ;
string lastName ;
getline (cin,firstName );
getline (cin,lastName );
,Joe Hernandez 23”
28
Interactive I/O
in an interactive program the user enters
information while the program is executing
before the user enters data,a prompt should be
provided to explain what type of information
should be entered
after the user enters data,the value of the data
should be printed out for verification,This is
called echo printing
that way,the user will have the opportunity to
check for erroneous data
29
Prompting for Interactive I/O
cout <<,Enter part number,,<< endl ; // prompt
cin >> partNumber ;
cout <<,Enter quantity ordered,,<< endl ;
cin >> quantity ;
cout <<,Enter unit price,,<< endl ;
cin >> unitPrice ;
totalPrice = quantity * unitPrice ; // calculate
cout <<,Part #,<< partNumber << endl ; // echo
cout <<,Quantity:,<< quantity << endl ;
cout <<,Unit Cost,$,<< setprecision(2)
<< unitPrice << endl ;
cout <<,Total Cost,$,<< totalPrice << endl ;
30
Noninteractive Input/Output
Many programs are written using noninteractive I/O
Example,batch processing
In batch processing,the user and the computer do not
Interact while the program running.The method is most
effective when a program is going to input or output large
amounts of data.
31
Diskette Files for I/O
your variable
(of type ifstream)
your variable
(of type ofstream)
disk file
“A:\myInfile.dat”
disk file
“A:\myOut.dat”
executing
program
input data output data
#include <fstream>
32
To Use Disk I/O,you must
use #include <fstream>
choose valid identifiers for your filestreams
and declare them
open the files and associate them with disk
names
use your filestream identifiers in your I/O
statements (using >> and <<,manipulators,
get,ignore)
close the files
33
Statements for Using Disk I/O
#include <fstream>
ifstream myInfile; // declarations
ofstream myOutfile;
myInfile.open(“A:\\myIn.dat”); // open files
myOutfile.open(“A:\\myOut.dat”);
myInfile.close( ); // close files
myOutfile.close( );
34
What does opening a file do?
associates the C++ identifier for your file with
the physical (disk) name for the file
if the input file does not exist on disk,open is
not successful
if the output file does not exist on disk,a new
file with that name is created
if the output file already exists,it is erased
places a file reading marker at the very
beginning of the file,pointing to the first
character in it
35
Map Measurement Case Study
You want a program to determine
walking distances between 4 sights in the
city,Your city map legend says one inch
on the map equals 1/4 mile in the city,
Read from a file the 4 measured
distances between sights on the map and
the map scale,
Output to a file the rounded (to the
nearest tenth) walking distances between
the 4 sights.
36
// ***************************************************
// Walk program using file I/O
// This program computes the mileage (rounded to nearest
// tenth of mile) for each of 4 distances,using input
// map measurements and map scale.
// ***************************************************
#include <iostream> // for cout,endl
#include <iomanip> // for setprecision
#include <fstream> // for file I/O
using namespace std;
float RoundToNearestTenth( float ); // declare function
An Example Program
Using File I/O
37
int main( )
{
float distance1; // First map distance
float distance2; // Second map distance
float distance3; // Third map distance
float distance4; // Fourth map distance
float scale; // Map scale (miles/inch)
float totMiles; // Total of rounded miles
float miles; // One rounded mileage
ifstream inFile; // First map distance
ofstream outFile; // Second map distance
outFile << fixed << showpoint // output file format
<< setprecision(1);
// Open the files
inFile.open(“walk.dat”);
outFile.open(“results.dat”);
38
// Get data from file
inFile >> distance1 >> distance2 >> distance3
>> distance4 >> scale;
totMiles = 0.0; // Initialize total miles
// Compute miles for each distance on map
miles = RoundToNearestTenth( distance1 * scale );
outFile << distance1 <<,inches on map is,
<< miles <<,miles in city.” << endl;
totMiles = totMiles + miles;
39
miles = RoundToNearestTenth( distance2 * scale );
outFile << distance2 <<,inches on map is,
<< miles <<,miles in city.” << endl;
totMiles = totMiles + miles;
miles = RoundToNearestTenth( distance3 * scale );
outFile << distance3 <<,inches on map is,
<< miles <<,miles in city.” << endl;
totMiles = totMiles + miles;
miles = RoundToNearestTenth( distance4 * scale );
outFile << distance4 <<,inches on map is,
<< miles <<,miles in city.” << endl;
totMiles = totMiles + miles;
40
// Write total miles to output file
outFile << endl <<,Total walking mileage is,
<< totMiles <<,miles.” << endl;
return 0 ; // Successful completion
}
// ***************************************************
float RoundToNearestTenth ( /* in */ float floatValue)
// Function returns floatValue rounded to nearest tenth.
{
return float(int(floatValue * 10.0 + 0.5)) / 10.0;
}
41
Run-Time Input of File Names
#include <string> // contains conversion function c_str
ifstream inFile;
string fileName;
cout <<,Enter input file name,,<< endl ; // prompt
cin >> fileName ;
// convert string fileName to a C string type
inFile.open( fileName.c_str( ) );
42
Input Failure
when a stream enters the fail state,further I/O
operations using that stream have no effect at
all,But the computer does not automatically
halt the program or give any error message
possible reasons for entering fail state include,
invalid input data (often the wrong type)
opening an input file that doesn’t exist
opening an output file on a diskette that is
already full or is write-protected
43
Software Design Methodologies
We describe two important design methodologies,
Object-oriented design
Functional decomposition
44
What is an object?
OBJECT
Operations
Data
set of functions
internal state
45
An object contains data
and operations
Private data:
accoutNumber
balance
OpenAccount
WriteCheck
MakeDeposit
IsOverdrawn
GetBalance
checkingAccount
46
Object-Oriented Design
A technique for developing a program in which
the solution is expressed in terms of objects --
self- contained entities composed of data and
operations on that data.
Private data
and function
<<
setf
.
.
.
Private data
and function
>>
get
.
.
.
ignore
cin cout
setw
47
More about OOD
languages supporting OOD include,C++,Java,
Smalltalk,Eiffel,CLOS,and Object-Pascal
a class is a programmer-defined data type and
objects are variables of that type
in C++,cin is an object of a data type (class) named
istream,and cout is an object of a class ostream,
Header files iostream and fstream contain
definitions of stream classes
a class generally contains private data and public
operations (called member functions)
48
Object-Oriented Design (OOD)
FOCUS is on entities called objects and operations on
those objects,all bundled together.
BEGINS by identifying the major objects in the problem,
and choosing appropriate operations on those objects,
UNITS are objects,Programs are collections of objects
that communicate with each other.
DATA plays a leading role,Algorithms are used to
implement operations on the objects and to enable
interaction of objects with each other.
49
Why use OOD with large
software projects?
objects within a program often model real-life
objects in the problem to be solved
many libraries of pre-written classes and objects
are available as-is for re-use in various programs
the OOD concept of inheritance allows the
customization of an existing class to meet
particular needs without having to inspect and
modify the source code for that class--this can
reduce the time and effort needed to design,
implement,and maintain large systems
50
Functional Decomposition
A technique for developing a program in
which the problem is divided into more
easily handled subproblems,the solutions
of which create a solution to the overall
problem.
In functional decomposition,we work from
the abstract (a list of the major steps in our
solution) to the particular (algorithmic
steps that can be translated directly into
code in C++ or another language),
51
Functional Decomposition
FOCUS is on actions and algorithms.
BEGINS by breaking the solution into a series of major
steps,This process continues until each subproblem
cannot be divided further or has an obvious solution,
UNITS are modules representing algorithms,A module
is a collection of concrete and abstract steps that
solves a subproblem,A module structure chart
(hierarchical solution tree) is often created,
DATA plays a secondary role in support of actions to be
performed.
52
Compute
Mileages
Write
Total Miles
Module Structure Chart
Main
Get Data
Round To
Nearest Tenth
Initialize
Total MilesOpen Files
53
A Perspective on Design
Functional decomposition and OOD are
not separate,disjoint techniques.
54
Two Programming
Methodologies
Functional Object-Oriented
Decomposition Design
FUNCTION
FUNCTION
FUNCTION
OBJECT
Operations
Data
OBJECT
Operations
Data
OBJECT
Operations
Data
55
Company Payroll Case Study
A small company needs an interactive
program to figure its weekly payroll,
The payroll clerk will input data for
each employee,Each employee?s
wages and data should be saved in a
secondary file,
Display the total wages for the week
on the screen.
56
Algorithm for Company Payroll
Program
Initialize total company payroll to 0.0
Repeat this process for each employee
1,Get the employee’s ID empNum
2,Get the employee’s hourly payRate
3,Get the hours worked this week
4,Calculate this week’s wages
5,Add wages to total company payroll
6,Write empNum,payRate,hours,wages to file
Write total company payroll on screen.
57
// ***************************************************
// Payroll program
// This program computes each employee’s wages and
// the total company payroll
// ***************************************************
#include <iostream> // for keyboard/screen I/O
#include <fstream> // for file I/O
using namespace std;
void CalcPay ( float,float,float& ) ;
const float MAX_HOURS = 40.0; // Maximum normal hours
const float OVERTIME = 1.5; // Overtime pay factor
Company Payroll Program
58
C++ Code Continued
int main( )
{
float payRate; // Employee’s pay rate
float hours; // Hours worked
float wages; // Wages earned
float total; // Total company payroll
int empNum; // Employee ID number
ofstream payFile; // Company payroll file
payFile.open(,payfile.dat” ); // Open file
total = 0.0; // Initialize total
59
cout <<,Enter employee number:,; // Prompt
cin >> empNum; // Read ID number
while ( empNum != 0 ) // While not done
{
cout <<,Enter pay rate:,;
cin >> payRate ; // Read pay rate
cout <<,Enter hours worked:,;
cin >> hours ; // and hours worked
CalcPay(payRate,hours,wages); // Compute wages
total = total + wages; // Add to total
payFile << empNum << payRate
<< hours << wages << endl;
cout <<,Enter employee number:,;
cin >> empNum; // Read ID number
}
60
cout <<,Total payroll is,
<< total << endl;
return 0 ; // Successful completion
}
// ***************************************************
void CalcPay ( /* in */ float payRate,
/* in */ float hours,
/* out */ float& wages )
// CalcPay computes wages from the employee’s pay rate
// and the hours worked,taking overtime into account
{
if ( hours > MAX_HOURS )
wages = (MAX_HOURS * payRate ) +
(hours - MAX_HOURS) * payRate * OVER_TIME;
else
wages = hours * payRate;
}
