Getting Data Into Programs

An advantage of programs is that they can be run many times using different sets of data.

A program must have some way of reading the data (this is called input).

An input stream is an endless sequence of characters coming into your program.

cin is associated with the standard input device (keyboard). It has the extraction operator >>.

The extraction operator >> takes two operands, cin and a variable.

Input Statement Syntax
and More

InputStatement

cin >> Variable >> Variable …;

cin >> length >> width; is equal to

cin >> length;

cin >> width;

Unlike the items specified in an output statement, which can be constants, variables, or complicated expressions, the items specified in an input statement can only be variable names.

Examples Using cin

int i, j, k; char ch; float x;

Statement Data Contents After Input

cin >> i; 32 i=32

Examples Using cin

int i, j, k; char ch; float x;

Statement Data Contents After Input

cin >> i; 32 i=32

cin >> i 4 60 i=4

Examples Using cin

int i, j, k; char ch; float x;

Statement Data Contents After Input

cin >> i; 32 i=32

cin >> i >> j; 4 60 i=4, j=60

Examples Using cin

int i, j, k; char ch; float x;

Statement Data Contents After Input

cin >> i; 32 i=32

cin >> i >> j; 4 60 i=4, j=60

cin >> i 25 A 16.9 i=25

Examples Using cin

int i, j, k; char ch; float x;

Statement Data Contents After Input

cin >> i; 32 i=32

cin >> i >> j; 4 60 i=4, j=60

cin >> i >> ch 25 A 16.9 i=25, ch=‘A’

Examples Using cin

int i, j, k; char ch; float x;

Statement Data Contents After Input

cin >> i; 32 i=32

cin >> i >> j; 4 60 i=4, j=60

cin >> i >> ch >> x; 25 A 16.9 i=25,ch=‘A’,x=16.9

Examples Using cin

int i, j, k; char ch; float x;

Statement Data Contents After Input

cin >> i; 32 i = 32

cin >> i >> j; 4 60 i = 4, j = 60

cin >> i >> ch >> x; 25 A 16.9 i=25,ch=‘A’,x=16.9

cin >> i >> ch >> x; 25

A

16.9 i=25,ch=‘A’,x=16.9

cin >> i >> ch >> x; 25A16.9 i=25,ch=‘A’,x=16.9

cin >> i 12 8 i = 12

The Reading Marker
and the Newline Character

The reading marker indicates the next character waiting to be read.

Each input line has an invisible end-of-line character (the newline character) that tells where one line ends and the next begins.

A newline character is inserted when you hit an enter or Return or when a program outputs an endl. It’s referred to as \n.

Examples:

ch = ‘\n’; or

cout << “Hello\n”;

(same as cout << “Hello” << endl;)

Exploring the Reading Marker

int i; char ch; float x;

Statements Contents After Input Marker Position

in the

Input Stream

25 A 16.9\n

Exploring the Reading Marker

int i; char ch; float x;

Statements Contents After Input Marker Position

in the

Input Stream

25 A 16.9\n

cin >> i; i = 25

Exploring the Reading Marker

int i; char ch; float x;

Statements Contents After Input Marker Position

in the

Input Stream

25 A 16.9\n

cin >> i; i = 25

cin >> ch; ch = ‘A’

Exploring the Reading Marker

int i; char ch; float x;

Statements Contents After Input Marker Position

in the

Input Stream

25 A 16.9\n

cin >> i; i = 25

cin >> ch; ch = ‘A’

cin >> x; x = 16.9

Another Reading
Marker Example

int i; char ch; float x;

Statements Contents After Marker Position in the

Input Input Stream

25\n

A\n

16.9\n

Another Reading
Marker Example

int i; char ch; float x;

Statements Contents After Marker Position in the

Input Input Stream

25\n

A\n

16.9\n

cin >> i; i = 25

Another Reading
Marker Example

int i; char ch; float x;

Statements Contents After Marker Position in the

Input Input Stream

25\n

A\n

16.9\n

cin >> i; i = 25

cin >> ch; ch = ‘A’

Another Reading
Marker Example

int i; char ch; float x;

Statements Contents After Marker Position in the

Input Input Stream

25\n

A\n

16.9\n

cin >> i; i = 25

cin >> ch; ch = ‘A’

cin >> x; x = 16.9

Reading Characters
withthe get Function

The >> operator skips any leading white-space characters (such as blanks and new-line characters) while looking for the next data value in the input stream.

Consider cin >> ch1 >> ch2; and an input stream of R 1. ch1 = ‘R’ ch2 = ‘1’ What if you wanted the blank also? You can’t do it with the extraction operator.

You can use the get function, which doesn’t skip any characters. cin.get(someChar);

The argument to the get function must be a character variable.

The get Function versus
the Extraction Operator

char ch1, ch2, ch3;

Statements Contents Marker Position in

After Input the Input Stream

A B\n

CD\n

cin >> ch1; ch1 = ‘A’

A B\n

CD\n

cin >> ch1; ch1 = ‘A’

The get Function versus
the Extraction Operator

char ch1, ch2, ch3;

Statements Contents Marker Position in

After Input the Input Stream

A B\n

CD\n

cin >> ch1; ch1 = ‘A’

cin >> ch2; ch2 = ‘B’

A B\n

CD\n

cin >> ch1; ch1 = ‘A’

cin >> ch2; ch2 = ‘B’

The get Function versus
the Extraction Operator

char ch1, ch2, ch3;

Statements Contents Marker Position in

After Input the Input Stream

A B\n

CD\n

cin >> ch1; ch1 = ‘A’

cin >> ch2; ch2 = ‘B’

cin >> ch3; ch3 = ‘C’

A B\n

CD\n

cin >> ch1; ch1 = ‘A’

cin >> ch2; ch2 = ‘B’

cin.get(ch3); ch3 = ‘\n’

Skipping Characters
with the ignore Function

The ignore function is used to skip charac-ters in the input stream.

It’s a function with two arguments

cin.ignore(200, ‘\n’);

The first argument is int, the second char. This statement says skip 200 characters or skip until you reach a newline character.

Reading String Data

The extraction operator can be used but not with any strings which have blanks embedded in them. (it stops reading when it encounters a whitespace)

There’s a function we can use: getline.

It stops when it reaches a newline character. (the newline character is consumed)

Example: getline(cin, myString);

Interactive Input/Output

//******************************************************************

// Prompts program

// This program demonstrates the use of input prompts

//******************************************************************

#include <iostream>

#include <iomanip>    // For setprecision()

using namespace std;

int main()

{

    int   partNumber;

    int   quantity;

    float unitPrice;

    float totalPrice;

    cout << fixed << showpoint            // Set up floating-pt.

         << setprecision(2);              //   output format

Interactive Input/Output

    cout << "Enter the part number:" << endl;          // Prompt

    cin >> partNumber;

    cout << "Enter the quantity of this part ordered:" // Prompt

         << endl;

    cin >> quantity;

    cout << "Enter the unit price for this part:"      // Prompt

         << endl;

    cin >> unitPrice;

    totalPrice = quantity * unitPrice;

    cout << "Part " << partNumber                      // Echo print

         << ", quantity " << quantity

         << ", at $ " << unitPrice << " each" << endl;

    cout << "totals $ " << totalPrice << endl;

    return 0;

}

Interactive I/O Example

Enter the part number:

4671

Enter the quantity of this part ordered:

10

Enter the unit price for this part:

27.25

Part 4671, quantity 10, at $ 27.25 each

Totals $ 272.50


	An advantage of programs is that they can be run many times using different sets of data.
	A program must have some way of reading the data (this is called input).
	An input stream is an endless sequence of characters coming into your program.
	cin is associated with the standard input device (keyboard). It has the extraction operator >>.
	The extraction operator >> takes two operands, cin and a variable.


	InputStatement
		cin >> Variable >> Variable …;
	cin >> length >> width; is equal to
	cin >> length;
	cin >> width;
	Unlike the items specified in an output statement, which can be constants, variables, or complicated expressions, the items specified in an input statement can only be variable names.


	int i, j, k; char ch; float x;
	Statement Data Contents After Input
	cin >> i; 32 i=32


	int i, j, k; char ch; float x;
	Statement Data Contents After Input
	cin >> i; 32 i = 32
	cin >> i >> j; 4 60 i = 4, j = 60
	cin >> i >> ch >> x; 25 A 16.9 i=25,ch=‘A’,x=16.9
	cin >> i >> ch >> x; 25
	A
	16.9 i=25,ch=‘A’,x=16.9
	cin >> i 25A16.9 i=25


	The reading marker indicates the next character waiting to be read.
	Each input line has an invisible end-of-line character (the newline character) that tells where one line ends and the next begins.
	A newline character is inserted when you hit an enter or Return or when a program outputs an endl. It’s referred to as \n.
	Examples:
		ch = ‘\n’; or
		cout << “Hello\n”;
		(same as cout << “Hello” << endl;)


	int i; char ch; float x;

	Statements Contents After Input Marker Position
	in the
	Input Stream

	25 A 16.9\n


	int i; char ch; float x;

	Statements Contents After Marker Position in the
	Input Input Stream
	25\n
	A\n
	16.9\n


	The >> operator skips any leading white-space characters (such as blanks and new-line characters) while looking for the next data value in the input stream.
	Consider cin >> ch1 >> ch2; and an input stream of R 1. ch1 = ‘R’ ch2 = ‘1’ What if you wanted the blank also? You can’t do it with the extraction operator.
	You can use the get function, which doesn’t skip any characters. cin.get(someChar);
	The argument to the get function must be a character variable.


	char ch1, ch2, ch3;
	Statements Contents Marker Position in
	After Input the Input Stream
	A B\n
	CD\n
	cin >> ch1; ch1 = ‘A’


	A B\n
	CD\n
	cin >> ch1; ch1 = ‘A’


	The ignore function is used to skip charac-ters in the input stream.
	It’s a function with two arguments
		cin.ignore(200, ‘\n’);
	The first argument is int, the second char. This statement says skip 200 characters or skip until you reach a newline character.


	The extraction operator can be used but not with any strings which have blanks embedded in them. (it stops reading when it encounters a whitespace)
	There’s a function we can use: getline.
	It stops when it reaches a newline character. (the newline character is consumed)
		Example: getline(cin, myString);


	//******************************************************************
	// Prompts program
	// This program demonstrates the use of input prompts
	//******************************************************************
	#include <iostream>
	#include <iomanip> // For setprecision()

	using namespace std;

	int main()
	{
	int partNumber;
	int quantity;
	float unitPrice;
	float totalPrice;

	cout << fixed << showpoint // Set up floating-pt.
	<< setprecision(2); // output format


	cout << "Enter the part number:" << endl; // Prompt
	cin >> partNumber;

	cout << "Enter the quantity of this part ordered:" // Prompt
	<< endl;
	cin >> quantity;

	cout << "Enter the unit price for this part:" // Prompt
	<< endl;
	cin >> unitPrice;

	totalPrice = quantity * unitPrice;
	cout << "Part " << partNumber // Echo print
	<< ", quantity " << quantity
	<< ", at $ " << unitPrice << " each" << endl;
	cout << "totals $ " << totalPrice << endl;
	return 0;
	}


	Enter the part number:
	4671
	Enter the quantity of this part ordered:
	10
	Enter the unit price for this part:
	27.25
	Part 4671, quantity 10, at $ 27.25 each
	Totals $ 272.50