Type * var;

_ Type _ * _ var;

Any _ underscore can be replaced with const in above statement.

below are three valid statements.

const int *ptr; // ptr is a pointer to constant int
int const *ptr; // ptr is a pointer to constant int (misleading but valid statement)

                                  +-----------+
                                  |   +-----+ |
                                  |   | +-+ | |
                                  |   | ^ | | |
                            int const *ptr; | |
                             ^    ^   ^   | | |
                             |    |   +---+ | |
                             |    +---------+ |
                             +----------------+

ptr is an pointer to constant int.

Example #2: Simple declaration

                                  +--------------+                       
                                  |   +--------+ |
                                  |   |    +-+ | |
                                  |   |    ^ | | |
                            int   * const ptr; | |
                             ^    ^   ^      | | |
                             |    |   +------+ | |
                             |    +------------+ |
                             +-------------------+

Question we ask ourselves: What is ptr? ptr is an...

int n = 10, m = 20;    
vector<int> v = {7, 5, 16, 8};
vector<int> vec(10); //with initial size 10, vec[i] can be used to insert elements. 
vector<int> vec2(10, 0); //intialized with zero.
vector<int> vec3(n);
vector<int> vec4(n, 0);
vector<vector<int>> grid(n, vector<int>(m));     // 2D vector of nxm
vector<vector<int>> grid2(n, vector<int>(m, 0)); //initialized with 0
vector<vector<int>> twoDVector;

1. begin() : returns an iterator pointing to the first element of the vector.
2. end()  : returns an iterator pointing to the theoretical element that follows the last element of vector.
3. rbegin() : returns a reverse iterator pointing to the last element of vector (reverse beginning). It moves from last to first element.
4. rend() : returns a reverse iterator pointing to the the pseudo(fake) element that precedes first element of vector (considered as reverse end).
5. cbegin() : returns a constant iterator pointing to the first element of vector.
6. cend() : returns a constant iterator pointing to the pseudo(fake) element that follows the last element of vector.
7. crbegin() : returns a constant reverse iterator pointing to the last element of vector (reverse beginning). It moves from last to first element
8. crend() : returns a constant reverse iterator pointing to the pseudo(fake) element  that precedes the first element of vector (considered as reverse end)

Member Functions:

 vector<int> vec;
 vec.push_back(1);
 cout <<"size: " << vec.size() << " max_size: " << vec.max_size() << " capacity: " << vec.capacity()<<endl;
 vec.push_back(2);
 cout << "size: " << vec.size() << " max_size: " << vec.max_size()<< " capacity: " << vec.capacity() << endl;
 vec.push_back(3);
 cout << "size: " << vec.size() << " max_size: " << vec.max_size()<< " capacity: " << vec.capacity() << endl;
 vec.push_back(4);
 cout << "size: " << vec.size() << " max_size: " << vec.max_size()<< " capacity: " << vec.capacity() << endl;
 vec.push_back(5);
 cout << "size: " << vec.size() << " max_size: " << vec.max_size()<< " capacity: " << vec.capacity() << endl;

  size: 1 max_size: 4611686018427387903 capacity: 1

  size: 2 max_size: 4611686018427387903 capacity: 2

  size: 4 max_size: 4611686018427387903 capacity: 4

size: 3 max_size: 4611686018427387903 capacity: 4

  size: 5 max_size: 4611686018427387903 capacity: 8

Element access:


reference operator [index] : returns a reference to the element at position ‘index’ in the vector

at(index) : returns a reference to the element at position ‘index’ in the vector

front() : returns a reference to the first element in the vector.

back() : returns a reference to the last element in the vector.

data() : returns a direct pointer to the memory array used internally by the vector to store its owned elements.




Modifiers:


assign() – It assigns new value to the vector elements by replacing old ones

push_back() – It push the elements into a vector from the back

pop_back() – It is used to pop or remove elements from a vector from the back.

insert() – It inserts new elements before the element at the specified position

erase() – It is used to remove elements from a container from the specified position or range.

swap() – It is used to swap the contents of one vector with another vector of same type. Sizes may differ.

clear() – It is used to remove all the elements of the vector container

emplace() – It extends the container by inserting new element at position

emplace_back() – It is used to insert a new element into the vector container, the new element is added to the end of the vector



ptr



All Vector Functions :


vector::begin() and vector::end()

vector rbegin() and rend()

vector::cbegin() and vector::cend()

vector::crend() and vector::crbegin()

vector::assign()

vector::at()

vector::back()

vector::capacity()

vector::clear()

vector::push_back()

vector::pop_back()

vector::empty()

vector::erase()

vector::size()

vector::swap()

vector::reserve()

vector::resize()

vector::shrink_to_fit()

vector::operator=

vector::operator[]

vector::front()

vector::data()

vector::emplace_back()

vector::emplace()

vector::max_size()

vector::insert()

 pair  Pair_name;

pair <int, string> pair_var;
pair_var.first = 1;
pair_var.second = "January";

pair <string, double> pair_var2;
pair_var2.first = "pi";
pair_var2.second = 3.14;

pair <string, float> golden_ratio_pair("goldenRatio", 1.6180);
pair <string, float> copy_pair(golden_ratio_pair);

cout<< golden_ratio_pair.first <<" : "<<golden_ratio_pair.second;
cout<< copy_pair.first <<" : "<<copy_pair.second;

pair <int, string> pair_var;

Output:
goldenRatio : 1.6180
goldenRatio : 1.6180

Member Functions

Pair_name = make_pair (value1,value2);

pair <string, int> pair_var3;
pair_var3 = make_pair("techBudhdha", 1);

pair <string, int> pair_var4("krishna", 2);
pair <string, int> pair_var5("techBudhdha", 1);

swap()
pair_var4.swap(pair_var5);orswap(pair_var4, pair_var5); Operators:operators(=, ==, !=, >=, <=, )  pair <int, int> pair_var1(5, 10); pair <int, int> pair_var2(7, 14); pair <int, int> pair_var3(5, 10);  if (pair_var1 == pair_var3)  // Trueif (pair_var1 == pair_var2)  // Falseif (pair_var1 != pair_var2)  // True <= and >= operator compare only first element of pair.  if (pair_var1 <= pair_var2) //Actual thing in backGround: pair_var1.first <= pair_var2.first : Trueif (pair_var1 >= pair_var2) //Actual thing in backGround: pair_var1.first >= pair_var2.first : Falsesame for  operators.
ptr