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# Input Iterator

Input iterator reads forward and is provided by istream
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### Key Facts

Gyroscopic Couple: The rate of change of angular momentum () = (In the limit).
• = Moment of Inertia.
• = Angular velocity
• = Angular velocity of precession.

Blaise Pascal (1623-1662) was a French mathematician, physicist, inventor, writer and Catholic philosopher.

Leonhard Euler (1707-1783) was a pioneering Swiss mathematician and physicist.

## Description

Input iterator moves only forward and may retrieve but not store values, provided by istream.

Input iterators can read elements only once. To progress to the next value or end of sequence, you increment it (post or pre-increment).

Two input iterators are equal if they occupy the same position. But this does NOT mean that they return the same value on element access!

## Operations

Expression Description
++i Steps forward and returns new position (when not null)
i++ Steps forward and returns old position (when not null)
i1==i2 Returns if i1 is equal to i2
i1!=2 Returns if i1 is not equal to i2
TYPE(i) Copies iterator (copy constructor)

## References

Example:
##### Example - istream_iterator and ostream_iterator
Problem
This program illustrates the use of the istream_iterator and ostream_iterator in conjunction with the copy algorithm to provide vector I/O.
Workings
#include <iostream>
#include <vector>
#include <algorithm>
#include <iterator>

int main()
{
int a[] = {1, 2, 3, 4, 5};
vector<int> v(a, a+5);
cout <<"\nInitial contents of v, displayed using the copy "
"algorithm to copy values from\nv to the standard output "
"with the help of an ostream_iterator:\n";
copy(v.begin(), v.end(), ostream_iterator<int>(cout, " "));

cout <<"\nNow we copy some values from standard input into a vector "
"\nusing the copy algorithm and an istream_iterator.\nEnter five "
"integer values, followed by your end-of-file character:\n";

copy(istream_iterator<int>(cin), istream_iterator<int>(), v.begin());

cin.ignore(80, '\n');
cin.clear();

cout << "\nFinal contents of v: ";
copy(v.begin(), v.end(), ostream_iterator<int>(cout, " "));

return 0;
}
Solution
Output:

Initial contents of v, displayed using the copy algorithm to copy values from
v to the standard output with the help of an ostream_iterator:
1 2 3 4 5

Now we copy some values from standard input into a vector
using the copy algorithm and an istream_iterator.
Enter five integer values, followed by your end-of-file character:
2 4 6 8 10
^Z

Final contents of v: 2 4 6 8 10
References