1. Collections Intro What is the STL? Templates, collections, & iterators
Adapted from Dr. Mary Eberlein

2. Data Structures
Collection or data structure: an object that stores data
elements: objects that are stored
collections can be ordered or unordered
some collections allow duplicate elements
Common operations: insert, size, isEmpty...
Good to know how to build collections (implementation)
Often use an available collection rather than implementing it yourself (and learn to use it effectively)
You use an iphone proficiently, but you don't necessarily understand internal function.

3. Type Parameters (templates)
Collection<type> name;
specify type of elements in triangle brackets
Called a type parameter – you get a parameterized class, or template class
type can be any data type: int, char, string, user-defined type...
Example: vector<int> v;
If you pass an object in C++ (without the &) it's passed by value – C++ makes a complete copy of its contents, rather than sharing its location. Objects are passed by value by default, not be reference. Making copies of objects is usually slow – you probably don't want this. So:
int computeSum(Something<int>& s) { ...
Have to pass by reference if you want function tmodify object also.

4. STL: Standard Template Library
STL: library of collections and algorithms for C++
Many use templates
container classes (set, list, stack, vector, queue...)
algorithms
iterators
STL

5. VECTOR

6. Won't Arrays Do? Arrays: fixed size – not easily resized
array doesn't "know" its own size
array index out of bounds errors not caught
don't support useful operations like:
inserting/deleting elements at front/middle/back of array
reversing order of elements
searching or sorting
preventing duplicate elements from being added
Arrays don't have many features. Not very powerful.
Go right ahead and exceed bound of array and access random garbage in memory

7. Vector vector (aka list): collection of elements with 0-based indexing
add elements anywhere in vector
automatic resizing as needed
vector has a size (current # of elements)
template class – create vectors of different types
No need to allocate/delete memory for vector
Header: #include<vector>
Recall: all of standard library in namespace std
vector<int> myVector; // vector of ints
vector<string> strVec; // vector of strings
Don't have to worry about resizing yourself.

8. Example Vector member function at():
C++ Array Example:
int size = 10;
int myArr[10];
int *arrPtr = new int[size];
for(int i = 0; i < 10; i++){
myArr[i] = i;
arrPtr[i] = i; }
delete [] arrPtr;
Vector member function at():
similar to indexing with [], but checks index validity
Resizing is handled for you when necessary
C++ Vector Example:
#include <vector>
using namespace std;
...
int size = 10;
// 10 ints in array, init to 0
vector<int> myArr(size);
for(int i = 0; i < size; i++)
myArr[i] = i;
// Don't need to delete!
Vectors have advantages of static and dynamically allocated array – it takes a non constant size like the dyn allocated array and ia automatically deleted like the static one.
Vector uses [] to allow indexing like arrays.

9. STL vector vector<int> v; // empty vector Member functions:
push_back(value): insert element at the end of the vector
v.push_back(3); // 3 added at end of v
v.push_back(5); // 5 added at end of v
at(index): return element at specified index
int x = v.at(0); // 3
size(): returns number of elements in vector
int numElts = v.size(); // 2
front(): returns reference to first element of vector
int& num = v.front(); // 3
back(): returns reference to last element of vector

10. STL iterator iterator: object that iterates over a data structure
pointer-like object that can be incremented (++), dereferenced (*), compared to another iterator (!=)
stores current position within data structure
used to traverse over the elements in a collection
iterator generated by STL member functions like begin() and end()
begin(): returns iterator pointing to 1st element of ordered collection (e.g., vector)
end(): returns iterator which is past the end of the collection

11. Iterator A collection has a begin and end iterator to front and back
Advance one element: iter++
Go back one element: iter--
Access element the iterator is next to: *iter
vector<int> v;
...
// loop over vector elements and print them
for(vector<int>::iterator it = v.begin();
it != v.end(); it++) {
cout << *it << endl; }

12. Iterator Example // for-each loop – implicit iterator (C++11)
vector<int> v;
...
for(int k : v) {
cout << k << endl; }

13. Iterator Example
Some container member functions take an iterator argument to indicate position
Example for vector: insert, erase
vector<int> v;
...
for(vector<int>::iterator it = v.end();
it != v.begin(); it--) {
if(*it % 2 == 0) {
it = v.erase(it); // delete element at this position }

14. STL Algorithms Many algorithms Example: sorting vectors
#include<algorithm>
vector<string> vec;
vec.push_back("hello"); vec.push_back("world");
vec.push_back("bye");
sort(v.begin(), v.end());