C++ Programming:
From Problem Analysis
to Program Design, Fourth Edition
Chapter 3: Input/Output
Objectives
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, putback, and peek
C++ Programming: From Problem Analysis to Program Design, Fourth Edition
Objectives (continued)
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
C++ Programming: From Problem Analysis to Program Design, Fourth Edition
I/O Streams and Standard I/O
Devices
I/O: sequence of bytes (stream of bytes) from
source to destination
Bytes are usually characters, unless program
requires other types of information
Stream: sequence of characters from source
to destination
Input stream: sequence of characters from an
input device to the computer
Output stream: sequence of characters from
the computer to an output device
C++ Programming: From Problem Analysis to Program Design, Fourth Edition
I/O Streams and Standard I/O
Devices (continued)
Use iostream header file to extract
(receive) data from keyboard and send output
to the screen
Contains definitions of two data types:
istream - input stream
ostream - output stream
Has two variables:
cin - stands for common input
cout - stands for common output
C++ Programming: From Problem Analysis to Program Design, Fourth Edition
I/O Streams and Standard I/O
Devices (continued)
To use cin and cout, the preprocessor
directive #include <iostream> must be
used
Variable declaration is similar to:
istream cin;
ostream cout;
Input stream variables: type istream
Output stream variables: type ostream
C++ Programming: From Problem Analysis to Program Design, Fourth Edition
cin and the Extraction Operator
>>
The syntax of an input statement using cin
and the extraction operator >> is:
The extraction operator >> is binary
Left-side operand is an input stream variable
Example: cin
Right-side operand is a variable
C++ Programming: From Problem Analysis to Program Design, Fourth Edition
cin and the Extraction Operator
>> (continued)
No difference between a single cin with
multiple variables and multiple cin
statements with one variable
When scanning, >> skips all whitespace
Blanks and certain nonprintable characters
>> distinguishes between character 2 and
number 2 by the right-side operand of >>
If type char or int (or double), the 2 is
treated as a character or as a number 2
C++ Programming: From Problem Analysis to Program Design, Fourth Edition
cin and the Extraction Operator
>> (continued)
Entering a char value into an int or double
variable causes serious errors, called input
failure
C++ Programming: From Problem Analysis to Program Design, Fourth Edition
cin and the Extraction Operator
>> (continued)
When reading data into a char variable
>> skips leading whitespace, finds and stores
only the next character
Reading stops after a single character
To read data into an int or double variable
>> skips leading whitespace, reads + or - sign
(if any), reads the digits (including decimal)
Reading stops on whitespace non-digit
character
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10
cin and the Extraction Operator
>> (continued)
C++ Programming: From Problem Analysis to Program Design, Fourth Edition
11
Using Predefined Functions in a
Program
Function (subprogram): set of instructions
When activated, it accomplishes a task
main executes when a program is run
Other functions execute only when called
C++ includes a wealth of functions
Predefined functions are organized as a
collection of libraries called header files
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13
Using Predefined Functions in a
Program (continued)
Header file may contain several functions
To use a predefined function, you need the
name of the appropriate header file
You also need to know:
Function name
Number of parameters required
Type of each parameter
What the function is going to do
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14
Using Predefined Functions in a
Program (continued)
To use pow (power), include cmath
Two numeric parameters
Syntax: pow(x,y) = xy
x and y are the arguments or parameters
In pow(2,3), the parameters are 2 and 3
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15
Using Predefined Functions in a
Program (continued)
Sample Run:
Line
Line
Line
Line
Line
1:
4:
5:
7:
9:
2 to the power of 6 = 64
12.5 to the power of 3 = 1953.13
Square root of 24 = 4.89898
u = 181.019
Length of str = 20
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17
cin and the get Function
The get function
Inputs next character (including whitespace)
Stores in memory location indicated by its
argument
The syntax of cin and the get function:
varChar
Is a char variable
Is the argument (parameter) of the function
C++ Programming: From Problem Analysis to Program Design, Fourth Edition
18
cin and the ignore Function
ignore: discards a portion of the input
The syntax to use the function ignore is:
intExp is an integer expression
chExp is a char expression
If intExp is a value m, the statement says to
ignore the next m characters or all characters
until the character specified by chExp
C++ Programming: From Problem Analysis to Program Design, Fourth Edition
19
putback and peek Functions
putback function
Places previous character extracted by the
get function from an input stream back to that
stream
peek function
Returns next character from the input stream
Does not remove the character from that
stream
C++ Programming: From Problem Analysis to Program Design, Fourth Edition
20
putback and peek Functions
(continued)
The syntax for putback:
istreamVar: an input stream variable (cin)
ch is a char variable
The syntax for peek:
istreamVar: an input stream variable (cin)
ch is a char variable
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21
The Dot Notation Between I/O
Stream Variables and I/O Functions
In the statement
cin.get(ch);
cin and get are two separate identifiers
separated by a dot
Dot separates the input stream variable name
from the member, or function, name
In C++, dot is the member access operator
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22
Input Failure
Things can go wrong during execution
If input data does not match corresponding
variables, program may run into problems
Trying to read a letter into an int or double
variable will result in an input failure
If an error occurs when reading data
Input stream enters the fail state
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23
The clear Function
Once in a fail state, all further I/O statements
using that stream are ignored
The program continues to execute with
whatever values are stored in variables
This causes incorrect results
The clear function restores input stream to
a working state
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Output and Formatting Output
Syntax of cout when used with <<
Expression is evaluated
Value is printed
Manipulator is used to format the output
Example: endl
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setprecision Manipulator
Syntax:
Outputs decimal numbers with up to n
decimal places
Must include the header file iomanip:
#include <iomanip>
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26
fixed Manipulator
fixed outputs floating-point numbers in a
fixed decimal format
Example: cout << fixed;
Disable by using the stream member function
unsetf
Example: cout.unsetf(ios::fixed);
The manipulator scientific is used to
output floating-point numbers in scientific
format
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showpoint Manipulator
showpoint forces output to show the
decimal point and trailing zeros
Examples:
cout << showpoint;
cout << fixed << showpoint;
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28
setw
Outputs the value of an expression in specific
columns
cout << setw(5) << x << endl;
If number of columns exceeds the number of
columns required by the expression
Output of the expression is right-justified
Unused columns to the left are filled with
spaces
Must include the header file iomanip
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Additional Output Formatting
Tools
Additional formatting tools that give you more
control over your output:
setfill manipulator
left and right manipulators
unsetf manipulator
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setfill Manipulator
Output stream variables can use setfill to
fill unused columns with a character
Example:
cout << setfill('#');
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left and right Manipulators
left: left-justifies the output
Disable left by using unsetf
right: right-justifies the output
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Types of Manipulators
Two types of manipulators:
With parameters
Without parameters
Parameterized: require iomanip header
setprecision, setw, and setfill
Nonparameterized: require iostream
header
endl, fixed, showpoint, left, and flush
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Input/Output and the string
Type
An input stream variable (cin) and >>
operator can read a string into a variable of
the data type string
Extraction operator
Skips any leading whitespace characters and
reading stops at a whitespace character
The function getline
Reads until end of the current line
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File Input/Output
File: area in secondary storage to hold info
File I/O is a five-step process
1. Include fstream header
2. Declare file stream variables
3. Associate the file stream variables with the
input/output sources
4. Use the file stream variables with >>, <<, or
other input/output functions
5. Close the files
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Programming Example: Movie
Ticket Sale and Donation to Charity
A theater owner agrees to donate a portion of
gross ticket sales to a charity
The program will prompt the user to input:
Movie name
Adult ticket price
Child ticket price
Number of adult tickets sold
Number of child tickets sold
Percentage of gross amount to be donated
C++ Programming: From Problem Analysis to Program Design, Fourth Edition
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Programming Example: I/O
Inputs: movie name, adult and child ticket
price, # adult and child tickets sold, and
percentage of the gross to be donated
Program output:
-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*
Movie Name: ....................... Journey to Mars
Number of Tickets Sold: ...........
2650
Gross Amount: ..................... $ 9150.00
Percentage of Gross Amount Donated:
Amount Donated: ................... $
10.00%
915.00
Net Sale: ......................... $ 8235.00
C++ Programming: From Problem Analysis to Program Design, Fourth Edition
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Programming Example: Problem
Analysis
The program needs to:
1.
2.
3.
4.
5.
Get the movie name
Get the price of an adult ticket price
Get the price of a child ticket price
Get the number of adult tickets sold
Get the number of child tickets sold
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Programming Example: Problem
Analysis (continued)
6. Calculate the gross amount
grossAmount = adultTicketPrice *
noOfAdultTicketsSold + childTicketPrice *
noOfChildTicketsSold;
7. Calculate the amount donated to the charity
amountDonated = grossAmount *
percentDonation / 100;
8. Calculate the net sale amount
netSale = grossAmount amountDonated;
9. Output the results
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Programming Example: Variables
string movieName;
double adultTicketPrice;
double childTicketPrice;
int
noOfAdultTicketsSold;
int
noOfChildTicketsSold;
double percentDonation;
double grossAmount;
double amountDonated;
double netSaleAmount;
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Programming Example:
Formatting Output
First column is left-justified
When printing a value in the first column, use
left
Numbers in second column are right-justified
Before printing a value in the second column,
use right
Use setfill to fill the empty space between
the first and second columns with dots
C++ Programming: From Problem Analysis to Program Design, Fourth Edition
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Programming Example:
Formatting Output (continued)
In the lines showing gross amount, amount
donated, and net sale amount
Use blanks to fill space between the $ sign
and the number
Before printing the dollar sign
Use setfill to set the filling character to
blank
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Programming Example: Main
Algorithm
1. Declare variables
2. Set the output of the floating-point to:
Two decimal places
Fixed
Decimal point and trailing zeros
3. Prompt the user to enter a movie name
4. Input movie name using getline because
it might contain spaces
5. Prompt user for price of an adult ticket
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Programming Example: Main
Algorithm (continued)
6.
7.
8.
9.
Input price of an adult ticket
Prompt user for price of a child ticket
Input price of a child ticket
Prompt user for the number of adult tickets
sold
10. Input number of adult tickets sold
11. Prompt user for number of child tickets sold
12. Input the number of child tickets sold
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Programming Example: Main
Algorithm (continued)
13. Prompt user for percentage of the gross
amount donated
14. Input 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
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Summary
Stream: infinite sequence of characters from a
source to a destination
Input stream: from a source to a computer
Output stream: from a computer to a
destination
cin: common input
cout: common output
To use cin and cout, include iostream
header
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46
Summary (continued)
get reads data character-by-character
putback puts last character retrieved by get
back to the input stream
ignore skips data in a line
peek returns next character from input
stream, but does not remove it
Attempting to read invalid data into a variable
causes the input stream to enter the fail state
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47
Summary (continued)
The manipulators setprecision, fixed,
showpoint, setw, setfill, left, and
right can be used for formatting output
Include iomanip for the manipulators
setprecision, setw, and setfill
File: area in secondary storage to hold info
Header fstream contains the definitions of
ifstream and ofstream
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