I am not understanding how he has declared the array

See more:

C++

// A generic safe array example.
#include <iostream>
#include <cstdlib>
using namespace std;
const int SIZE = 10;
template <class AType> class atype {
AType a[SIZE];
public:
atype() {
register int i;
for(i=0; i<SIZE; i++) a[i] = i;
}
AType &operator[](int i);
};
// Provide range checking for atype.
template <class AType> AType &atype<atype>::operator[](int i)
{
if(i<0 || i> SIZE-1) {
cout << "\nIndex value of ";
cout << i << " is out-of-bounds.\n";
exit(1);
}
return a[i];
}
int main()
{
atype<int> intob; // integer array
atype<double> doubleob; // double array
int i;
cout << "Integer array: ";
for(i=0; i<SIZE; i++) intob[i] = i;
for(i=0; i<SIZE; i++) cout << intob[i] << " ";
cout << '\n';
cout << "Double array: ";
for(i=0; i<SIZE; i++) doubleob[i] = (double) i/3;
for(i=0; i<SIZE; i++) cout << doubleob[i] << " ";
cout << '\n';
intob[12] = 100; // generates runtime error
return 0;
}

What I have tried:

I have searched for it in the web.