Program to create Custom Vector Class in C++

The task is to implement a custom vector class similar to the STL vector with following functions:

int push_back(data): adds an element(of any data_type) to the end of array and also returns the number of elements in that vector
data_type pop_back(): removes an element from the end of array, also returns the popped element
int size() const: returns the current size of vector

Recommended: Please try your approach on {IDE} first, before moving on to the solution.

Below program implements a custom vector class in C++ with above mentioned functionalities:

// C++ program to implement Custom Vector 
// class 
#include "iostream" 
#define ll long long 
using namespace std; 
  
// Template class to create vector of 
// different data_type 
template <typename DT> 
class GenericMyVector { 
private: 
    DT* arr; 
  
    // Variable to store the current capacity 
    // of the vector 
    ll capacity; 
  
    // Variable to store the length of the 
    // vector 
    ll length; 
  
public: 
    explicit GenericMyVector(ll = 100); 
  
    // Function that returns the number of 
    // elements in array after pushing the data 
    ll push_back(DT); 
  
    // function that returns the popped element 
    DT pop_back(); 
  
    // Function that return the size of vector 
    ll size() const; 
    DT& operator[](ll); 
  
    // Iterator Class 
    class iterator { 
    private: 
        // Dynamic array using pointers 
        DT* ptr; 
  
    public: 
        explicit iterator() 
            : ptr(nullptr) 
        { 
        } 
        explicit iterator(DT* p) 
            : ptr(p) 
        { 
        } 
        bool operator==(const iterator& rhs) const
        { 
            return ptr == rhs.ptr; 
        } 
        bool operator!=(const iterator& rhs) const
        { 
            return !(*this == rhs); 
        } 
        DT operator*() const
        { 
            return *ptr; 
        } 
        iterator& operator++() 
        { 
            ++ptr; 
            return *this; 
        } 
        iterator operator++(int) 
        { 
            iterator temp(*this); 
            ++*this; 
            return temp; 
        } 
    }; 
  
    // Begin iterator 
    iterator begin() const; 
  
    // End iterator 
    iterator end() const; 
}; 
  
// Template class to return the size of 
// vector of different data_type 
template <typename DT> 
GenericMyVector<DT>::GenericMyVector(ll n) 
    : capacity(n), arr(new DT[n]), length(0) 
{ 
} 
  
// Template class to insert the element 
// in vector 
template <typename DT> 
ll GenericMyVector<DT>::push_back(DT data) 
{ 
    if (length == capacity) { 
        DT* old = arr; 
        arr = new DT[capacity = capacity * 2]; 
        copy(old, old + length, arr); 
        delete[] old; 
    } 
    arr[length++] = data; 
    return length; 
} 
  
// Template class to return the popped element 
// in vector 
template <typename DT> 
DT GenericMyVector<DT>::pop_back() 
{ 
    return arr[length-- - 1]; 
} 
  
// Template class to return the size of 
// vector 
template <typename DT> 
ll GenericMyVector<DT>::size() const
{ 
    return length; 
} 
  
// Template class to return the element of 
// vector at given index 
template <typename DT> 
DT& GenericMyVector<DT>::operator[](ll index) 
{ 
    // if given index is greator than the 
    // size of vector print Error 
    if (index >= length) { 
        cout << "Error: Array index out of bound"; 
        exit(0); 
    } 
  
    // else return value at that index 
    return *(arr + index); 
} 
  
// Template class to return begin iterator 
template <typename DT> 
typename GenericMyVector<DT>::iterator  
                      GenericMyVector<DT>::begin() const
{ 
    return iterator(arr); 
} 
  
// Template class to return end iterator 
template <typename DT> 
typename GenericMyVector<DT>::iterator  
                        GenericMyVector<DT>::end() const
{ 
    return iterator(arr + length); 
} 
  
// Template class to display element in 
// vector 
template <typename V> 
void display_vector(V& v) 
{ 
    // Declare iterator 
    typename V::iterator ptr; 
    for (ptr = v.begin(); ptr != v.end(); ptr++) { 
        cout << *ptr << ' '; 
    } 
    cout << '\n'; 
} 
  
// Driver code 
int main() 
{ 
    cout << "For Integer data_type" << endl; 
  
    GenericMyVector<int> v; 
    v.push_back(5); 
    v.push_back(6); 
    v.push_back(7); 
    v.push_back(8); 
    v.push_back(9); 
    v.push_back(10); 
    v.push_back(11); 
    v.push_back(12); 
  
    // Declare iterator for traversal in 
    // vector v 
    GenericMyVector<int>::iterator it; 
  
    // Function called to display element in 
    // vector in v 
    cout << "Element in vector v : "; 
    display_vector(v); 
  
    // Print the size of vector v 
    cout << "size: " << v.size() << endl; 
  
    // Print Element at index 2 
    cout << "v[2]: " << v[2] << '\n'; 
  
    // Pop an element and print it 
    cout << "Popped Element: " << v.pop_back() << '\n'; 
    display_vector(v); 
  
    cout << endl; 
  
    cout << "For Char data_type" << endl; 
  
    GenericMyVector<char> c; 
    c.push_back('a'); 
    c.push_back('b'); 
    c.push_back('c'); 
    c.push_back('d'); 
    c.push_back('e'); 
    c.push_back('f'); 
    c.push_back('g'); 
    c.push_back('h'); 
  
    // Declare iterator for traversal in 
    // vector c 
    GenericMyVector<char>::iterator it1; 
  
    // Function called to display element in 
    // vector in c 
    cout << "Element in vector c : "; 
    display_vector(c); 
  
    // Print the size of vector c 
    cout << "size: " << c.size() << '\n'; 
  
    // Print Element at index 2 
    cout << "c[2]: " << c[2] << '\n'; 
  
    // Pop an element and print it 
    cout << "pop: " << c.pop_back() << '\n'; 
  
    // Function called to display element in 
    // vector in c 
    cout << "Element in vector c : "; 
    display_vector(c); 
    return 0; 
} 

Output:

For Integer data_type
Element in vector v : 5 6 7 8 9 10 11 12 
size: 8
v[2]: 7
Popped Element: 12
5 6 7 8 9 10 11 

For Char data_type
Element in vector c : a b c d e f g h 
size: 8
c[2]: c
pop: h
Element in vector c : a b c d e f g

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My Personal Notes

Recommended: Please try your approach on {IDE} first, before moving on to the solution.

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