Notes
Outline
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 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 >> x; 25 A 16.9 i=25,ch=‘A’,x=16.9
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
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 25A16.9 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 >> 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 25A16.9 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
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
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
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 >> j 12 8 i = 12, j = 8
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 >> j >> x; 12 8 i = 12, j = 8
(Computer waits for
a third number)
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 >> j >> x; 12 8 i = 12, j = 8
(Computer waits for
a third number)
cin >> i 46 32.4 15 i = 46
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 >> j >> x; 12 8 i = 12, j = 8
(Computer waits for
a third number)
cin >> i >> x; 46 32.4 15 i = 46, x = 32.4
(15 is held for
later input)
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