CHAPTER 3 INPUT/OUTPUT

About This Presentation

Title:

CHAPTER 3 INPUT/OUTPUT

Description:

The following statement sets the output to be right-justified on the standard output device: cout – PowerPoint PPT presentation

Number of Views:447

Avg rating:3.0/5.0

Slides: 107

Provided by: abc7266

Category:

more less

Transcript and Presenter's Notes

Title: CHAPTER 3 INPUT/OUTPUT

1
CHAPTER 3 INPUT/OUTPUT
2

In this chapter, you will
Learn what a stream is and examine input and
output streams
Explore how to read data from the standard input
device
Learn how to use predefined functions in a
program
Explore how to use the input stream functions
get, ignore, fill, putback, and peek
Become familiar with input failure
Learn how to write data to the standard output
device
Discover how to use manipulators in a program to
format output
Learn how to perform input and output operations
with the string data type
Become familiar with file input and output

Input/Output Streams
I/O is a sequence of bytes, called a stream of
bytes, from the source to the destination.
The bytes are usually characters, unless the
program requires other types of information such
as a graphic image or digital speech.
A stream is a sequence of characters from the
source to the destination.
Input Stream A sequence of characters from an
input device to the computer.
Output Stream A sequence of characters from
the computer to an output device.

I/O STREAMS AND STANDARD I/O DEVICES
To extract (that is, receive) data from keyboard
and send output to the screen, every C program
must use the header file iostream.
This header file, iostream, contains definitions
of two data types, istream (input stream) and
ostream (output stream).
The header file, iostream, contains the
declaration of two variables, cin (stands for
common input), pronounced see-in, and cout
(stands for common output), pronounced see-out,
and the declaration is similar to the following
C statements
istream cin
ostream cout
To use cin and cout every C program must use
the preprocessor directive
include ltiostreamgt

Variables of the type istream are called input
stream variables.
Variables of the type ostream are called output
stream variables.
A stream variable is either an input stream
variable or an output stream variable.

cin and the Extraction Operator (gtgt)
Consider the following C statement
cingtgtpayRate
If you type 15.50, the value stored in payRate
after the execution of this statement is 15.50.
The extraction operator gtgt is binary. The
left-hand operand is an input stream variable
such as cin. The right-hand operand is a variable
of a simple data type.
The purpose of an input statement is to read and
store values in a memory location and only
variables refer to memory locations, the items
(that is, right hand operand in the case of the
extraction operator, gtgt) must be a variable in an
input statement.

The syntax of an input statement using cin and
the extraction operator gtgt is
cingtgtvariablegtgtvariable...

Every occurrence of gtgt extracts the next data
item from the input stream.
You can read both payRate and hoursWorked via a
single cin statement by using the following code
cingtgtpayRategtgthoursWorked
There is no difference between the preceding cin
statement and the following two cin statements.
cingtgtpayRate
cingtgthoursWorked
When scanning for the next input, gtgt skips all
whitespaces.
Whitespace characters consist of blanks and
certain nonprintable characters, such as tabs and
the newline character.

Whether the input is
15.50 48.30
or
15.50 48.30
or
15.50
48.30
The input statement
cingtgtpayRategtgthoursWorked
would store 15.50 in payRate and 48.30 in
hoursWorked.

Suppose the input is 2. How does gtgt distinguish
between character 2 and the number 2?
This is distinguished by the right hand operand
of gtgt.
If the right hand operand, that is, variable, is
of type char, input 2 is treated as character 2
(recall that in this case, the ASCII value of 2
will be stored). And if the right-hand operand is
of the type int (or double), input 2 is treated
as the number 2.
Now consider the input 25 and the statement
cingtgta
where a is a variable of some simple data
type.
If a is of the data type char, then only the
single character 2 will be stored in a.
If a is of the data type, say int, then 25 will
be stored in a.
If a is of the type double, then the input 25 is
converted to a decimal number with zero decimal
part.

Consider the statement
cingtgta
where a is a variable of some simple data type.

When reading data into a char variable, after
skipping any leading whitespace characters, the
extraction operator gtgt finds and stores only the
next character reading stops after a single
character.
To read data into an int or double variable,
after skipping all leading whitespace characters
and reading the plus or minus sign (if any), the
extraction operator gtgt reads the digits of the
number, including the decimal point for
floating-point variables, and stops when it finds
a whitespace character or a character other than
a digit.

Example 3-1
int a,b
double z
char ch,ch1,ch2
Statement Input Value Stored in Memory
1 cingtgtch A ch'A'
2 cingtgtch AB ch'A', 'B' is held for
later input
3 cingtgta 48 a48
4 cingtgta 46.35 a46, .35 is held for
later input
5 cingtgtz 74.35 z74.35
6 cingtgtz 39 z39.0
7 cingtgtzgtgta 65.78 38 z65.78, a38
8 cingtgtagtgtb 4 60 a4, b60
9 cingtgtagtgtchgtgtz 57 A 26.9 a57, ch'A', z26.9

10 cingtgtagtgtchgtgtz 57 A
26.9 a57, ch'A', z26.9
11 cingtgtagtgtchgtgtz 57
A
26.9 a57, ch'A', z26.9
12 cingtgtagtgtchgtgtz 57A26.9 a57, ch'A', z26.9
13 cingtgtzgtgtchgtgta 36.78B34 z36.78, ch'B',
a34
14 cingtgtzgtgtchgtgta 36.78
B34 z36.78, ch'B', a34
15 cingtgtagtgtbgtgtz 11 34 a11, b34, Computer
waits for the next number

16 cingtgtagtgtz 46 32.4 68 a46, z32.4, 68 is
held for later input
17 cingtgtchgtgta 256 ch'2', a56
18 cingtgtagtgtch 256 a256, computer waits
for the input value for ch.
19 cingtgtch1gtgtch2 A B ch1 'A', ch2 'B
During program execution, when entering character
data such as letters, you do not enter the single
quotes around the character.
Entering a char value into an int or double
variable causes serious errors, called input
failure.

USING PREDEFINED FUNCTIONS IN A PROGRAM
A function, also called subprogram, is a set of
instructions.
When a function is activated, that is, executed,
it accomplishes something.
The function main is executed automatically when
we execute a program.
Other functions are executed only when they are
called.
The programming language C comes with a wealth
of functions.

Predefined functions are organized as a
collection of libraries, called header files.
A particular header file may contain several
functions.
To use a particular function, you need to know
the name of the function and a few other things.
A very useful function, pow, called the power
function, can be used to calculate xy in a
program. That is, pow(x,y) xy.
pow(2,3) 23 8 and pow(4,0.5) 40.5 2.
The numbers x and y that you use in the function
pow are called the arguments or parameters of the
function pow.
In pow(2,3), the parameters are 2 and 3.
An expression such as pow(2,3) is called a
function call.
The header file cmath contains the specification
of the function pow.

To use a predefined function in a program, you
need to know the name of the header file
containing the specification of the function and
include that header file in the program.
In addition, you need to know the name of the
function, the number of parameters the function
takes, and the type of each parameter. You must
also be aware of what the function is going to
do.
To use the function pow, you must include the
header file cmath.
The function pow has two parameters, both of
which are numbers. The function calculates the
first parameter to the power of the second
parameter.

cin and the get Function
Consider the declaration
char ch1, ch2
int num
and the input
A 25
Now consider the statement
cingtgtch1gtgtch2gtgtnum
When the computer executes this statement, A is
stored in ch1, blank is skipped by gtgt, 2 is
stored in ch2, and 5 is stored in num.
If we intended to store A in ch1, blank in ch2
and 25 in num? It is clear that we can not use
the extraction operator gtgt.

The get function inputs the very next character
(including whitespaces) from the input stream and
stores in the memory location indicated by its
argument.
The syntax of cin together with the get function
to read a character is
cin.get(varChar)
where varChar is a char variable.
varChar is called the argument or parameter of
the function.
The next input character is stored in varChar.

Now, again, consider the input
A 25
We can effectively use the get function as
follows
cin.get(ch1)
cin.get(ch2)
cingtgtnum
to store A in ch1, blank in ch2, and 25 in num.
The above set of statements is equivalent to the
following
cingtgtch1
cin.get(ch2)
cingtgtnum

cin and the ignore Function
To process partial data, say with in a line, we
can effectively use the ignore function to
discard some portion of the input.
The syntax to use the function ignore is
cin.ignore(intExp,chExp)
where intExp is an integer expression yielding
an integer value and chExp is a char expression.
Suppose intExp yields a value, say m. This
statement says, ignore the next m characters or
until the character specified by chExp, whichever
comes first.

Consider the following statement
cin.ignore(100,'\n')
The execution of this statement will ignore the
next 100 characters or until the newline
character is found whichever comes first.
The execution of the statement
cin.ignore(100,'A')
will result in ignoring the first 100 characters
or until the character 'A' is found, whichever
comes first.

Example 3-2
int a,b
Suppose the input is
25 67 89 43 72
12 78 34
Consider the statements
cingtgta
cin.ignore(100,'\n')
cingtgtb
The first statement cingtgta stores 25 in a.
The second statement, cin.ignore(100,'\n')
discards all of the remaining numbers in the
first line.
The third statement cingtgtb stores 12 (from the
next line) in b.

Example 3-3
char ch1,ch2
Suppose the input is
Hello there. My name is Mickey.
Now consider the statements
cingtgtch1
cin.ignore(100,'.')
cingtgtch2
The first statement cingtgtch1 stores 'H' in ch1.
The second statement, cin.ignore(100,'.' )
results in ignoring all characters until '.'
(period).
The third statement cingtgtch2 stores 'M' (from
the same line) in ch2.

The peek and the putback Functions
The putback function places the previous
character extracted by the get function from an
input stream back to that stream.
The peek function returns the next character from
the input stream but it does not remove the
character from that stream, that is, the next
input character would be the same.
The syntax to use the function putback is
istreamVar.putback(ch)
where istreamVar is an input stream variable,
such as cin, and ch is a char variable.
The syntax to use the function peek is
ch istreamVar.peek()
where istreamVar is an input stream variable,
such as cin, and ch is a char variable.

Example 3-4
//Functions peek and putback
include ltiostreamgt
using namespace std
int main()
char ch
coutltlt"Line 1 Enter a string " //Line 1
cin.get(ch) //Line 2
coutltltendl //Line 3
coutltlt"Line 4 After first cin.get(ch) "
ltlt"ch "ltltchltltendl //Line 4

cin.get(ch) //Line 5
coutltlt"Line 6 After second cin.get(ch) "
ltlt"ch "ltltchltltendl //Line 6
cin.putback(ch) //Line 7
cin.get(ch) //Line 8
coutltlt"Line 9 After putback and then "
ltlt"cin.get(ch) ch "ltltchltltendl //Line 9
ch cin.peek() //Line 10
coutltlt"Line 11 After cin.peek() ch "
ltltchltltendl //Line 11

cin.get(ch) //Line 12
coutltlt"Line 13 After cin.get(ch) ch "
ltltchltltendl //Line 13
return 0
Sample Run In this sample run, the user input is
in red.
Line 1 Enter a string abcd
Line 4 After first cin.get(ch) ch a
Line 6 After second cin.get(ch) ch b
Line 9 After putback and then cin.get(ch) ch
b
Line 11 After cin.peek() ch c
Line 13 After cin.get(ch) ch c

The Dot Notation Between I/O Stream Variables and
I/O Functions A Precaution
To use the get function we used statements such
as
cin.get(ch)
Missing dot will result in compile time error.
For example, in the statement
cin.get(ch)
cin and get are two separate identifiers, while
in the statement
cinget(ch)
cinget becomes a new identifier and the compiler
might be trying to resolve the problem of an
undeclared identifier in the program. Similarly,
missing parentheses will result in compile time
error.

Several functions are associated with an istream
variable, each doing a specific job.
The functions get, ignore, and so on are members
of the data type istream.
Called the dot notation, the dot separates the
input stream variable name from the member, or
function, name.
In C, the dot is an operator called the member
access operator.
C has a special name for the data types istream
and ostream.
The data types istream and ostream are called
classes.
The variables cin and cout also have special
names, called objects. cin is called an istream
object
cout is called an ostream object.
Stream variables are called stream objects.

INPUT FAILURE
Many things can go wrong during program
execution.
A program that is syntactically correct might
produce incorrect results.
Suppose that a part-time employees paycheck is
calculated by using the following formula
wages payRate hoursWorked
If you accidentally type in place of , the
calculated wages would be incorrect, even though
the statement containing a is syntactically
correct.

What about an attempt to read invalid data?
What would happen if you tried to input a letter
into an int variable?
If the input data did not match the corresponding
variables, the program would run into problems.
Trying to read a letter into an int or double
variable would result in an input failure.

Consider the following statements
int a, b, c
double x
If the input is
W 54
then the statement
cingtgtagtgtb
would result in an input failure because you are
trying to input the character 'W' into the int
variable a.

If the input is
35 67.93 48 78
then the input statement
cingtgtagtgtxgtgtb
would result in storing 35 in a, 67.93 in x, and
48 in b.
Now consider the following read statement with
the previous input (the input with three values)
cingtgtagtgtbgtgtc
This statement stores 35 in a and 67 in b. The
reading stops at . (the decimal point). Because
the next variable c is of the data type int, the
computer tries to read . into c, which is an
error. The input stream then enters a state
called the fail state.

What actually happens when the input stream
enters the fail state?
Once an input stream enters a fail state, all
further I/O statements using that stream are
ignored.
Unfortunately, the program quietly continues to
execute with whatever values are stored in
variables and produce incorrect results.

Example 3-5
//Input Failure program
include ltiostreamgt
using namespace std
int main()
int a 10 //Line 1
int b 20 //Line 2
int c 30 //Line 3
int d 40 //Line 4
coutltlt"Line 5 Enter four integers "
//Line 5
cingtgtagtgtbgtgtcgtgtd //Line 6
coutltltendl //Line 7

coutltlt"Line 8 The numbers you entered are"
ltltendl //Line 8
coutltlt"Line 9 a "ltltaltlt", b "ltltb
ltlt", c "ltltcltlt", d "ltltdltltendl //Line 9
return 0
Sample Run 1 The user input is in red.
Line 5 Enter four integers 34 K 67 28
Line 8 The numbers you entered are
Line 9 a 34, b 20, c 30, d 40

The clear Function
When an input stream enters the fail state, the
system ignores all further I/O using that stream.
You can use the stream function clear to restore
the input stream to a working state.
The syntax to use the function clear is
istreamVar.clear()
Here istreamVar is an input stream variable, such
as cin.

OUTPUT AND FORMATTING OUTPUT
Syntax of cout when used together with the
insertion operator ltlt is
coutltltexpression or manipulator
ltltexpression or manipulator...
expression is evaluated, its value is printed,
and manipulator is used to format the output.
The simplest manipulator that you have used so
far is endl, which is used to move the cursor to
the beginning of the next line.

setprecision
The general form of setprecision is
setprecision(n)
where n is the number of decimal places.
The statement
coutltltsetprecision(2)
will output all decimal numbers up to two decimal
places until it is reset.
To use the manipulator setprecision, the program
must include the header file iomanip.
include ltiomanipgt

fixed
To output floating-point numbers in a fixed
decimal format, you use the manipulator fixed.
The following statement sets the output of
floating-point numbers in a fixed decimal format
on the standard output device
coutltltfixed
After the preceding statement executes, all
floating-point numbers are displayed in the
fixed-decimal format until the manipulator fixed
is disabled.

You can disable the manipulator fixed by using
the stream member function unsetf.
The following statement disables the manipulator
fixed on the standard output device, you use
cout.unsetf(iosfixed)
After the manipulator fixed is disabled, the
output of the floating-point numbers return to
their default settings.
The manipulator scientific is used to output
floating-point numbers in scientific format.

showpoint
If the decimal part of a decimal number is zero,
then when you instruct the computer to output the
decimal number in a fixed decimal format, the
output may not show the decimal point and the
decimal part.
To force the output to show the decimal point and
trailing zeros, you use the manipulator
showpoint.
The following statement sets the output of
decimal numbers with a decimal point and trailing
zeros on the standard input device
coutltltshowpoint
The following statement sets the output of a
floating-point number in a fixed decimal format
with the decimal point and trailing zeros on the
standard output device
coutltltfixedltltshowpoint

Example 3-7
//Example setprecision, fixed, showpoint
include ltiostreamgt
include ltiomanipgt
using namespace std
int main()
double x,y,z
x 15.674 //Line 1
y 235.73 //Line 2
z 9525.9864 //Line 3
coutltltfixedltltshowpoint //Line 4

coutltltsetprecision(2)
ltlt"Line 5 setprecision(2)"ltltendl //Line 5
coutltlt"Line 6 x "ltltxltltendl //Line 6
coutltlt"Line 7 y "ltltyltltendl //Line 7
coutltlt"Line 8 z "ltltzltltendl //Line 8
coutltltsetprecision(3)
ltlt"Line 9 setprecision(3)"ltltendl //Line 9
coutltlt"Line 10 x "ltltxltltendl //Line 10
coutltlt"Line 11 y "ltltyltltendl //Line 11
coutltlt"Line 12 z "ltltzltltendl //Line 12

coutltltsetprecision(4)
ltlt"Line 13 setprecision(4)"ltltendl //Line 13
coutltlt"Line 14 x "ltltxltltendl //Line 14
coutltlt"Line 15 y "ltltyltltendl //Line 15
coutltlt"Line 16 z "ltltzltltendl //Line 16
coutltlt"Line 17 "
ltltsetprecision(3)ltltxltlt" "
ltltsetprecision(2)ltltyltlt" "
ltltsetprecision(4)ltltzltltendl //Line 17
return 0

Output
Line 5 setprecision(2)
Line 6 x 15.67
Line 7 y 235.73
Line 8 z 9525.99
Line 9 setprecision(3)
Line 10 x 15.674
Line 11 y 235.730
Line 12 z 9525.986
Line 13 setprecision(4)
Line 14 x 15.6740
Line 15 y 235.7300
Line 16 z 9525.9864
Line 17 15.674 235.73 9525.9864

The stream function setf can be used to set
fixed, scientific, and showpoint.
In this case, fixed, scientific, and showpoint
are referred to as iosfixed, iosscientific,
and iosshowpoint, respectively, and are called
formatting flags.
Both the flags iosfixed and iosscientific are
part of iosfloatfield, which is a data type in
C.
When setting the fixed or scientific flag, to
ensure that only either the iosfixed or
iosscientific flag is set, you must pass
iosfloatfield as a second argument to the
function setf.
cout.setf(iosfixed,iosfloatfield)

The following statement sets the flag
iosshowpoint to output floating-point numbers
with a decimal point and trailing zeros on the
standard output device
cout.setf(iosshowpoint)

C provides the manipulator setiosflags, to set
the flags iosfixed, iosscientific, and
iosshowpoint.
To use the manipulator setiosflags , the program
must include the header file iomanip.
The following statement uses the manipulator
setiosflags to set the flags iosfixed and
iosshowpoint on the standard output device
coutltltsetiosflags(iosfixed)
coutltltsetiosflags(iosshowpoint)

You can specify more than one flag in the
manipulator setiosflags by separating the flags
with the symbol .
The following statement sets both the flags
iosfixed and iosshowpoint on the standard
output device
coutltltsetiosflags(iosfixed iosshowpoint)

setw
setw(n) - output the value of the next expression
in n columns.
The output is right justified.
If the number of specified columns is less than
the number of columns required by the output,
then the output is automatically expanded to the
required number of columns.
Unlike setprecision, which controls the output of
all floating-point numbers until it is reset,
setw controls the output of only the next
expression.
To use the manipulator setw, the program must
include the header file iomanip.

Example 3-8
//Example setw
include ltiostreamgt
include ltiomanipgt
using namespace std
int main()
int x 19 //Line 1
int a 345 //Line 2
double y 76.384 //Line 3
coutltltfixedltltshowpoint //Line 4

coutltlt"12345678901234567890"ltltendl //Line 5
coutltltsetw(5)ltltxltltendl //Line 6
coutltltsetw(5)ltltaltltsetw(5)ltlt"Hi"
ltltsetw(5)ltltxltltendlltltendl //Line 7
coutltltsetprecision(2) //Line 8
coutltltsetw(6)ltltaltltsetw(6)ltlty
ltltsetw(6)ltltxltltendl //Line 9
coutltltsetw(6)ltltxltltsetw(6)ltlta
ltltsetw(6)ltltyltltendlltltendl //Line 10
coutltltsetw(5)ltltaltltxltltendl //Line 11
coutltltsetw(2)ltltaltltsetw(4)ltltxltltendl //Line 12
return 0

Output
12345678901234567890
19
345 Hi 19
345 76.38 19
19 345 76.38
34519
345 19

ADDITIONAL OUTPUT FORMATTING TOOLS
fill and setfill
In the manipulator setw if the number of columns
specified are more than the number of columns
required by the expression, the output of the
expression is right justified and the unused
columns to the left are filled with spaces.
The output stream variables, such as cout, can
use the function fill and/or the manipulator
setfill to fill the unused columns with a
character other than the space.
The syntax to use the function fill is
ostreamVar.fill(ch)
where ostreamVar is an output stream variable
and ch is a character. For example, the statement
cout.fill('')
sets the filling character to '' on the standard
output screen.

The syntax to use the manipulator setfill is
ostreamVarltltsetfill(ch)
where ostreamVar is an output stream variable and
ch is a character.
The statement
coutltltsetfill('')
sets the filling character to ''.

Example 3.9
//Example fill and setfill
include ltiostreamgt
include ltiomanipgt
using namespace std
int main()
int x 15 //Line 1
int y 7634 //Line 2
coutltlt"12345678901234567890"ltltendl //Line 3
coutltltsetw(5)ltltxltltsetw(7)ltlty
ltltsetw(8)ltlt"Warm"ltltendl //Line 4

coutltltsetw(5)ltltxltltsetw(7)ltltsetfill('')
ltltyltltsetw(8)ltlt"Warm"ltltendl //Line 7
coutltltsetw(5)ltltsetfill('_at_')ltltx
ltltsetw(7)ltltsetfill('')ltlty
ltltsetw(8)ltltsetfill('')ltlt"Warm"
ltltendl //Line 8
cout.fill(' ') //Line 9
coutltltsetw(5)ltltxltltsetw(7)ltlty
ltltsetw(8)ltlt"Warm"ltltendl //Line 10
return 0
Output
12345678901234567890
15 7634 Warm
157634Warm
157634Warm
_at__at__at_157634Warm

The left and right Manipulators
To left-justify the output, you use the
manipulator left.
The syntax to set the manipulator left is
ostreamVarltltleft
where ostreamVar is an output stream variable.
The following statement sets the output to be
left-justified on the standard output device
coutltltleft

You can disable the manipulator left by using the
stream function unsetf. The syntax to disable the
manipulator left is
ostreamVar.unsetf(iosleft)
where ostreamVar is an output stream variable.
Disabling the manipulator left returns the output
to the settings of the default output format.
The following statement disables the manipulator
left on the standard output device
cout.unsetf(iosleft)

The syntax to set the manipulator right is
ostreamVarltltright
where ostreamVar is an output stream variable.
The following statement sets the output to be
right-justified on the standard output device
coutltltright

Example 3-10
//Example left justification
include ltiostreamgt
include ltiomanipgt
using namespace std
int main()
int x 15 //Line 1
int y 7634 //Line 2
coutltltleft //Line 3
coutltlt"12345678901234567890"ltltendl //Line 4
coutltltsetw(5)ltltxltltsetw(7)ltlty
ltltsetw(8)ltlt"Warm"ltltendl //Line 5

coutltltsetw(5)ltltxltltsetw(7)ltlty
ltltsetw(8)ltlt"Warm"ltltendl //Line 7
coutltltsetw(5)ltltxltltsetw(7)ltltsetfill('')ltlty
ltltsetw(8)ltlt"Warm"ltltendl //Line 8
coutltltsetw(5)ltltsetfill('_at_')ltltx
ltltsetw(7)ltltsetfill('')ltlty
ltltsetw(8)ltltsetfill('')ltlt"Warm"ltltendl
//Line 9
cout.unsetf(iosleft) //Line 10
cout.fill(' ') //Line 11
coutltltsetw(5)ltltxltltsetw(7)ltlty
ltltsetw(8)ltlt"Warm"ltltendl //Line 12
return 0

Output
12345678901234567890
15 7634 Warm
157634Warm
157634Warm
15_at__at__at_7634Warm
15 7634 Warm

The flush Function
Both the manipulator endl and the newline escape
sequence \n position the cursor at the beginning
of the next line on the output device.
When a program sends output to an output device,
the output first goes to the buffer in the
computer.
Whenever the buffer becomes full, the output is
sent to the output device.
As soon as the manipulator endl is encountered,
the output from the buffer is sent to the output
device immediately, even if the buffer is not
full.
The manipulator endl positions the cursor at the
beginning of the next line on an output device
and helps clear the buffer.
It is quite possible that sometimes you may not
see the entire output because when the program
terminates, the buffer at that time may not be
full.

In C, you can use the function flush to clear
the buffer, even if the buffer is not full.
In contrast to the manipulator endl, the function
flush does not move the cursor to the beginning
of the next line.
The syntax to use the flush function is
ostreamVar.flush()
where ostreamVar is an output stream variable,
such as cout.
Just like endl, the function flush can be used as
a manipulator. In such a case, flush is used in
an output statement without the parentheses. For
example, the following statement sends the output
from the buffer to the standard output device
coutltltflush

Example 3-11
Consider the following statements in which num is
an int variable
coutltlt"Enter an integer " //Line 1
cingtgtnum //Line 2
coutltltendl //Line 3
The statement at Line 1 outputs the following
text
Enter an integer
After outputting this line, the cursor stays
positioned after the colon.
The output of the statement at Line 1 first goes
to the buffer.
If the buffer is not full, this line of text
might not be displayed.
You could put the manipulator endl at the end of
the statement at Line 1. However, by doing so,
after printing the line of text, the cursor is
positioned at the beginning of the next line.

The user is prompted to enter the number in the
following line
Suppose that the statement at Line 1 is replaced
by the following statement
coutltlt"Enter an integer "ltltflush //Line 1
In this case, the line of text,
Enter an integer
is displayed on the standard output device even
if the buffer is not full. Moreover, after
outputting the line of text, the cursor stays
positioned after the colon the user will then
enter the number after the colon.

To use stream functions such as get, ignore,
fill, clear, and setf in a program, the program
must include the header file iostream.
There are two types of manipulators those with
parameters and those without parameters.
Manipulators with parameters are called
parameterized stream manipulators.
Manipulators such as setprecision, setw, setfill,
and setiosflags are parameterized.
Manipulators such as endl, fixed, scientific,
showpoint, and left are without parameters.
Because flush can also be used as a manipulator
without any arguments, flush is a manipulator
without parameters, too.

To use a parameterized stream manipulatorthat
is, a stream manipulator with parametersin a
program, you must include the header file
iomanip.
Manipulators without parameters are part of the
iostream header file and, therefore, do not
require inclusion of the header file iomanip.

Input/Output and the string Type
You can use an input stream variable, such as
cin, and the extraction operator gtgt to read a
string into a variable of the data type string.
If the input is the string "Shelly", the
following code stores this input into the string
variable name
string name // declaration
cingtgtname // input statement
The extraction operator skips any leading
whitespace characters and that reading stops at a
whitespace character.
You cannot use the extraction operator to read
strings that contain blanks.

If the input is
Alice Wonderland
the value of the variable name after the
following statement executes is "Alice"
cingtgtname
To read a string containing blanks, you can use
the function getline .
The syntax to use the function getline is
getline(istreamVar, strVar)
where istreamVar is an input stream variable and
strVar is a variable of the type string. The
reading is delimited by the newline character,
'\n'.

The function getline reads until it reaches the
end of the current line.
The newline character is also read but not stored
in the string variable.
Consider the following statement
string myString
If the input is 29 characters,
bbbbHello there. How are you?
where b represents a blank, after the statement
getline(cin,myString)
the value of myString is
myString " Hello there. How are you?"

File Input/Output
File An area in secondary storage used to hold
information.
For file I/O, the following steps are necessary.
1. Include the header file fstream in the
program. So the following statement is needed.
include ltfstreamgt
2. Declare file (fstream) variables. For example
the statements
ifstream inData
ofstream outData
declare the variable inData for input and
outData for output. That is, inData is an input
(file) stream variable and outData is an output
(file) stream variable.

3. Open Files
The general syntax for opening a file is
fileStreamVariable.open(sourceName,
fileOpeningMode)
Here fileStreamVariable is a file stream
variable, sourceName is the name of the
input/output file, and fileOpeningMode specifies
the mode in which the file is to be opened.

78
(No Transcript)
79

Suppose declaration of Step 2.
Suppose that the input data is stored in a file
called prog.dat on a floppy disk in drive A.
Save the output in a file called prog.out on a
floppy disk in drive A.
The following statements associate inData with
prog.dat and outData with prog.out.
inData.open("Aprog.dat") //open input file
outData.open("Aprog.out") //open output file

Step 4
Use the (file) stream variable together with gtgt
or ltlt or with other functions for input/Output.
The syntax for using gtgt or ltlt with file variables
is exactly similar to the syntax of cin and cout.
The statement
inDatagtgtpayRate
reads the data from the file prog.dat and stores
it in the variable payRate
The statement
outDataltlt"The pay check is "ltltpayltltendl
stores the output line, which is The pay check
is 565.78, in the file prog.out. Here we are
assuming that the pay was calculated as 565.78.

Close File
inData.close()
outData.close()

include ltfstreamgt
//Add additional header files you use
using namespace std
int main()
//Declare file stream variables such as the
following
ifstream inData
ofstream outData
...
//Open files
inData.open("Aprog.dat") //open input file
outData.open("Aprog.out") // open output file
//Code for data manipulation
//Close files
inData.close()
outData.close()
return 0

PROGRAMMING EXAMPLE MOVIE TICKET SALE AND
DONATION TO CHARITY
A movie in a local theater is in great demand. To
help a local charity, the theater owner has
decided to donate a portion of the gross amount
generated from the movie to the charity. This
example designs and implements a program that
prompts the user to input the movie name, adult
ticket price, child ticket price, number of adult
tickets sold, number of child tickets sold, and
percentage of the gross amount to be donated to
the charity. The output of the program is as
follows.
-------------------------
---
Movie Name ....................... Duckey Goes
to Mars
Number of Tickets Sold ........... 2650
Gross Amount ..................... 9150.00
Percentage of Gross Amount Donated 10.00
Amount Donated ................... 915.00
Net Sale ......................... 8235.00

Input
The input to the program consists of the movie
name, adult ticket price, child ticket price,
number of adult tickets sold, number of child
tickets sold, and percentage of the gross amount
to be donated to the charity.
Output
The output is as shown above.

Problem Analysis and Algorithm Design
grossAmount adultTicketPrice
noOfAdultTicketsSold
childTicketPrice noOfChildTicketsSold
The formulas to calculate the amount donated and
the net sale amount are given below.
1. Get the movie name.
2. Get the price of an adult ticket price.
3. Get the price of a child ticket price.
4. Get the number of adult tickets sold.
5. Get the number of child tickets sold.
6. Get the percentage of the gross amount donated
to the charity.

7. Calculate the gross amount using the following
formula
grossAmount adultTicketPrice
noOfAdultTicketsSold
childTicketPrice
noOfChildTicketsSold
8. Calculate the amount donated to the charity
using the following formula
amountDonated grossAmount percentDonation
/ 100
9. Calculate the net sale amount using the
following formula
netSale grossAmount amountDonated

Variables
string movieName
double adultTicketPrice
double childTicketPrice
int noOfAdultTicketsSold
int noOfChildTicketsSold
double percentDonation
double grossAmount
double amountDonated
double netSaleAmount

Formatting Output
In the output, the first column is left-justified
and the numbers in the second column are
right-justified.
When printing a value in the first column, the
manipulator left is used before printing a value
in the second column, the manipulator right is
used.
The empty space between the first and second
columns is filled with dots the program uses the
manipulator setfill to accomplish this goal.
In the lines showing the gross amount, amount
donated, and net sale amount, the space between
the sign and the number is filled with blank
spaces.
Before printing the dollar sign, the program uses
the manipulator setfill to set the filling
character to blank.

The following statements accomplish the desired
output
coutltlt"---------------"
ltlt"-------------"ltltendl
coutltltsetfill('.')ltltleftltltsetw(35)ltlt"Movie Name
"
ltltrightltlt" "ltltmovieNameltltendl
coutltltleftltltsetw(35)ltlt"Number of Tickets Sold "
ltltsetfill(' ')ltltrightltltsetw(10)
ltltnoOfAdultTicketsSold noOfChildTicketsSold
ltltendl
coutltltsetfill('.')ltltleftltltsetw(35)ltlt"Gross
Amount "
ltltsetfill(' ')ltltrightltlt" "
ltltsetw(8)ltltgrossAmountltltendl
coutltltsetfill('.')ltltleftltltsetw(35)
ltlt"Percentage of Gross Amount Donated "
ltltsetfill(' ')ltltright
ltltsetw(9)ltltpercentDonationltlt''ltltendl

coutltltsetfill('.')ltltleftltltsetw(35)ltlt"Amount
Donated "
ltltsetfill(' ')ltltrightltlt" "
ltltsetw(8)ltltamountDonatedltltendl
coutltltsetfill('.')ltltleftltltsetw(35)ltlt"Net Sale "
ltltsetfill(' ')ltltrightltlt" "
ltltsetw(8)ltltnetSaleAmountltltendl

Main Algorithm
1. Declare the variables.
2. Set the output of the floating-point numbers
to two decimal places in a fixed decimal format
with a decimal point and trailing zeros.
Therefore, you need to include the header file
iomanip.
3. Prompt the user to enter a movie name.
4. Input (read) the movie name. Because the name
of a movie might contain more than one word (and,
therefore, might contain blanks), the program
uses the function getline to input the movie
name. Moreover, because the function getline also
reads the newline character, after entering the
movie name on a line, you need to press the Enter
key twice.
5. Prompt the user to enter the price of an adult
ticket.
6. Input (read) the price of an adult ticket.
7. Prompt the user to enter the price of a child
ticket.

8. Input (read) the price of a child ticket.
9. Prompt the user to enter the number of adult
tickets sold.
10. Input (read) the number of adult tickets
sold.
11. Prompt the user to enter the number of child
tickets sold.
12. Input (read) the number of child tickets
sold.
13. Prompt the user to enter the percentage of
the gross amount donated.
14. Input (read) the percentage of the gross
amount donated.
15. Calculate the gross amount.
16. Calculate the amount donated.
17. Calculate the net sale amount.
18. Output the results.

include ltiostreamgt
include ltiomanipgt
include ltstringgt
using namespace std
int main()
//Step 1
string movieName
double adultTicketPrice
double childTicketPrice
int noOfAdultTicketsSold
int noOfChildTicketsSold
double percentDonation
double grossAmount
double amountDonated
double netSaleAmount

coutltltfixedltltshowpointltltsetprecision(2)
//Step 2
coutltlt"Enter movie name "ltltflush //Step 3
getline(cin,movieName) //Step 4
coutltltendl
coutltlt"Enter the price of an adult ticket
"ltltflush //Step 5
cingtgtadultTicketPrice //Step 6
coutltltendl
coutltlt"Enter the price of a child ticket
"ltltflush //Step 7
cingtgtchildTicketPrice //Step 8
coutltltendl

coutltlt"Enter number of adult tickets sold
"ltltflush //Step 9
cingtgtnoOfAdultTicketsSold //Step 10
coutltltendl
coutltlt"Enter number of child tickets sold
"ltltflush //Step 11
cingtgtnoOfChildTicketsSold //Step 12
coutltltendl
coutltlt"Enter the percentage of donation
"ltltflush //Step 13
cingtgtpercentDonation //Step 14
coutltltendlltltendl
grossAmount adultTicketPrice
noOfAdultTicketsSold
childTicketPrice noOfChildTicketsSold
//Step 15

amountDonated grossAmount percentDonation /
100 //Step 16
netSaleAmount grossAmount - amountDonated
//Step 17
//Step 18 Output results
coutltlt"---------------"
ltlt"-------------"ltltendl
coutltltsetfill('.')ltltleftltltsetw(35)ltlt"Movie
Name "
ltltrightltlt" "ltltmovieNameltltendl
coutltltleftltltsetw(35)ltlt"Number of Tickets Sold
"
ltltsetfill(' ')ltltrightltltsetw(10)
ltltnoOfAdultTicketsSold noOfChildTicketsSold
ltltendl

coutltltsetfill('.')ltltleftltltsetw(35)ltlt"Gross
Amount "
ltltsetfill(' ')ltltrightltlt" "
ltltsetw(8)ltltgrossAmountltltendl
coutltltsetfill('.')ltltleftltltsetw(35)
ltlt"Percentage of Gross Amount Donated "
ltltsetfill(' ')ltltright
ltltsetw(9)ltltpercentDonationltlt''ltltendl
coutltltsetfill('.')ltltleftltltsetw(35)ltlt"Amount
Donated "
ltltsetfill(' ')ltltrightltlt" "
ltltsetw(8)ltltamountDonatedltltendl
coutltltsetfill('.')ltltleftltltsetw(35)ltlt"Net Sale
"
ltltsetfill(' ')ltltrightltlt" "
ltltsetw(8)ltltnetSaleAmountltltendl
return 0

Sample Run (In this sample run, the user input
is in red)
Enter movie name Duckey Goes to Mars
Enter the price of an adult ticket 4.50
Enter the price of a child ticket 3.00
Enter number of adult tickets sold 800
Enter number of child tickets sold 1850
Enter the percentage of donation 10
-------------------------
---
Movie Name ....................... Duckey Goes
to Mars
Number of Tickets Sold ........... 2650

PROGRAMMING EXAMPLE STUDENT GRADE
Write a program that reads a student ID followed
by five test scores. The program should output
the student ID, the five test scores, and the
average test score. Output the average test score
with two decimal places. Assume that the student
ID is a character.
The data to be read is stored in a file called
test.txt, and the file is stored on a floppy disk
in drive A. The output should be stored in a
file called testavg.out, and the output file
should be stored on the floppy disk in drive A.
Input A file containing the student ID and five
test scores.
Output The student ID, five test scores and the
average of the five test scores. The output is to
be saved in a file.

100

Problem Analysis and Algorithm Design
To find the average of five test scores, first we
add the five test scores and then divide the sum
by 5. Now, the input data is in the form student
ID followed by five test scores. Therefore, we
first read the student ID and then the five test
scores. This discussion translates in the
following algorithm
1. Read student ID and the five test score.
2. Output student ID and five test scores.
3. Calculate the average.
4. Output the average.
We will output the average test score in the
fixed decimal format with two decimal places.

101

Variables
ifstream inFile //input file stream variable
ofstream outFile //output file stream variable
int test1, test2, test3, test4, test5 //
variables
//to read five test scores
double average //variable to store average
//test score
char studentId //variable to store
//student ID

102

Main Algorithm
1. Declare the variables.
2. Open the input file.
3. Open the output file.
4. To output the floating-point numbers in a
fixed decimal format with a decimal point and
trailing zeros, set the manipulators fixed and
showpoint. Also, to output the floating-point
numbers with two decimal places, set the
precision to two decimal places.
5. Read the student ID.
6. Output the student ID.
7. Read the five test scores.
8. Output the five test scores.
9. Find the average test score.
10. Output the average test score.
11. Close the input and output files.