Day #1 of Learning DSA - Here is What I Learned

/** 
Task: To implement an automatically resizing vector
Functions:
	size() - number of items
	capacity() - number of items it can hold
	is_empty()
	at(index) - returns item at given index, blows up if index out of bounds
	push(item)
	insert(index, item) - inserts item at index, shifts that index's value and trailing elements to the right
	prepend(item) - can use insert above at index 0
	pop() - remove from end, return value
	delete(index) - delete item at index, shifting all trailing elements left
	remove(item) - looks for value and removes index holding it (even if in multiple places)
	find(item) - looks for value and returns first index with that value, -1 if not found
*/
 
#include <iostream>
using namespace std;
 
template<typename T> class Array{
	// arr is the integer pointer which stores the address of our vector
	T* arr;
	// capacity is the total storage available for the vector
	int _capacity;
	// current is the number of elements present in the vector
	int current;
	void resize(){
		if(current==_capacity){
			T* temp = new T[2 * _capacity];
			for(int i = 0; i < _capacity; i++){
				temp[i] = arr[i];
			}
			delete[] arr;
			_capacity *= 2;
			arr = temp;
		}
		if(current==_capacity/4){
			T* temp = new T[_capacity / 2];
			for(int i = 0; i < _capacity; i++){
				temp[i] = arr[i];
			}
			delete[] arr;
			_capacity = _capacity / 2;
			arr = temp;
		}
	}
	public: 
		Array(){
			arr = new T[1];
			_capacity = 1;
			current = 0;	
		}
		/**
		 * @return the number of items present in array 
		*/
		int size(){
			return current;
		} 
		/**
		 * @return the number of items array can hold 
		*/
		int capacity(){
			return _capacity;
		}
		/**
		 * @return whether the array is empty or not
		*/
		bool is_empty(){
			if(current==0)
				return true;
			return false;	
		}
		/**
		 * @param item - Adds item to the array
		*/
		void push(T item){
			if(current==_capacity){
				T* temp = new T[2 * _capacity];
				for(int i = 0; i < _capacity; i++){
					temp[i] = arr[i];
				}
				delete[] arr;
				_capacity *= 2;
				arr = temp;
			}
			arr[current] = item;
			current++;
		}
		/**
		 * @param index - index of item
		 * @return return the item at given index
		*/
		T at(int index){
			if(index < current){
				return arr[index];
			}
		} 
		/**
		 * @param index - index of item to be inserted
		 * @param item - item to be inserted
		*/
		void insert(int item, int index){
			// if index is equal to capacity
			// then this function is same as
			// push function defined earlier
			if(index == _capacity){
				push(item);
			}
			else{
				for(int i = this->current; i>=index; i--)
					arr[i] = arr[i-1];
				arr[index] = item;
				current++;
			}
		}
		/**
		 * @param item - item to be added
		*/
		void prepend(int item){
			insert(item, 0);
		}
		/**
		 * @return pops the last element and returns it
		*/
		T pop() {
			if(current > 0){
				current--;
				resize();
				return arr[current+1];
			}
		}
		/**
		 * Function to delete item at
		 * @param index index of the item to delete
		*/
		void deleteElement(int index){
			int temp = current;
			
			current--;
		}
		/**
		 * Function to remove all items that match given item
		 * @param item Item to remove. All matching items will be removed
		*/
		void remove(T item){
			const int s = this->size();
			for(int i = 0; i < s; i++){
				if(item == arr[i]){
					for(int j = i; j < s; j++){
						arr[j]=arr[j+1];
					}
					current--;
				}
			}
		}
		/**
		 * Function to find index of item
		 * @param item Item to look for
		*/
		int find(T item){
			int index = -1;
			for(int i = 0; i < current; i++){
				if(item == arr[i]){
					index = i;
					break;
				}
			}
			return index;
		}
		void print(){
			for(int i = 0; i < current; i++){
				cout << arr[i] << endl;
			}
		}
};
 
 
// Driver code
int main(){
	Array<int> arr;
		arr.push(3);
  	arr.prepend(2);
  	arr.insert(1,0);
  	arr.print();
  
  	arr.pop();
  	cout << "Is array empty: 0=False, 1=True: " << arr.is_empty() << endl;
  	cout << "Capacity of array: " << arr.capacity() << endl;
  	cout << "No. of elements in array: " << arr.size() << endl;
  	cout << "Element at position 1: " << arr.at(1) << endl;
  	cout << "Deleting element at position 1: " << endl;
  	arr.deleteElement(1);
  	arr.print();
  	arr.push(3);
    cout << "Removing all 3s from array: " << endl;
  	arr.remove(3);
  	arr.print();
}
/**
Output
1
2
3
Is array empty: 0=False, 1=True: 0
Capacity of array: 1
No. of elements in array: 2
Element at position 1: 2
Deleting element at position 1: 
1
Removing all 3s from array: 
1
*/