templated dynamic class with iterator

#include<bits/stdc++.h>
using namespace std;
template<typename T>
class mass{
    size_t size=0;
    size_t reserve=0;
    T* arr= nullptr;
    void increase(){
        if(reserve==0)++reserve;
        T* ptr=new T[reserve*2];
        for(int i=0;i<size;++i)
            ptr[i]=arr[i];
        delete[] arr;
        arr=ptr;
        reserve*=2;
    }
public:
    T& operator [](const int &pos){
        return arr[pos];
    }
    size_t get_size() {
        return size;
    }
    size_t get_reserve(){
        return reserve;
    }
    void add_last(const T& a){
        if(size==reserve)
            increase();
        arr[size]=a;
        ++size;
    }
    void delete_last(){
        --size;
    }
    void add(const int& pos,const T& a){
        if(size==reserve)
            increase();
        for(int i=size;i>=pos;--i){
            if(i==pos){
                arr[i]=a;
                continue;
            }
            arr[i]=arr[i-1];
        }
        ++size;
    }
    void _delete(const int& pos){
        for(int i=pos;i<size;++i){
            arr[i]=arr[i+1];
        }
        --size;
    }
    T get(const int& pos){
        return arr[pos];
    }
    void show(){
        for(int i=0;i<size;++i)
            cout<<arr[i]<<' ';
        cout<<'\n';
    }
    T* begin(){
        return arr;
    }
    T* end(){
        return &arr[size];
    }
    ~mass(){
        delete[] arr;
    }
    mass(const mass<T>& m){
        this->arr=new T[m.reserve];
        for(int i=0;i<m.size;++i)
            this->arr[i]=m.arr[i];
        this->size=m.size;
        this->reserve=m.reserve;
    }
    mass<T>& operator =(const mass<T>& m){
        delete[] this->arr;
        this->arr=new T[m.reserve];
        for(int i=0;i<m.size;++i)
            this->arr[i]=m.arr[i];
        this->size=m.size;
        this->reserve=m.reserve;
        return *this;
    }
    mass()= default;
};