IntArray arr(10);
for(int i = 0; 0 < 10; i++)
  a[i] = i * 10;

a[0] = 0, a[1] =10, a[2]=20.... so on

IntArray arr(-3, 10)

IntArray arr(6, 8)`

//---------------------Header file

#ifndef INTARRAY_H_
#define INTARRAY_H_

#include <iostream>


using namespace std;

class IntArray
{

private:
    int first;
    int last;
    int size;

    string arrName;
    int* arrPtr;


public:
    IntArray();
    int& operator[](int i);

    IntArray(int num);
    IntArray(int num1, int num2);

    int low();
    int high();
    void setName(string str);
    //streams
    friend istream& operator>>(istream& is, IntArray& d);
    friend ostream& operator<<(ostream& os, IntArray& d);

};

#endif /* INTARRAY_H_ */
//---------------------

#include "IntArray.h"



IntArray::IntArray(){
    size = 10;
    first = 0; last = 9;
    arrPtr = new int[size];
}

IntArray::IntArray(int num){
    size = num;
    first = 0; last = size-1;
    arrPtr = new int[size];
    //cout<<"n the size "<<size<<endl;
    //arrPtr[3] = 123;

    //ex = 3;
}

IntArray::IntArray(int num1, int num2){
    first = num1; last = num2;
    size = last - first + 1;
    //cout<<"n the size "<<size<<endl;
    arrPtr = new int[size];
}

int& IntArray::operator[](int i) {
    if (i >= (last+1)){
        cout<<"Error: Index out of range"<<endl;
        exit(1);
    }
    return arrPtr[i];
}

int IntArray::getInt(int i){
    return arrPtr[i];
}

//======================
int IntArray::low(){
    return first;
}
int IntArray::high(){
    return last;
}
//======================
//==========OUT stream==========

// for cout << justName<< endl;
ostream& operator<<(ostream& os, IntArray& aPtr) {
    for(int i = aPtr.low(); i <= aPtr.high(); i++){
        os << aPtr.arrName <<"[" << i << "] = " << aPtr[i] << " ";
    }

    return os;
}

void IntArray::setName(string str){
    arrName = str;
}

IntArray c(6, 8);
    for(int i = c.low(); i <= c.high(); i++)
        c[i] = i * 10;
    c.setName("c");
    cout << c << endl;
    csis << c << endl;
    IntArray e(c);
    e.setName("e");
    cout << e << endl;