Why classes are needed in C++?

What is access specifies?

When the memory space allocated to the class members?

Write the significance of Default constructors.

What will be the output of the following program?
# include < iostream >
# include < conio >
using namespace std
class add          //Global class
{
int a,b;
public:
int sum;
void getdata( )
{
a=5;
b=10;
sum = a+b;
}
} a1;             //globalobject
add a2; ,      //globalobject
int main( )
{
add a3;        //Local object for a global class
a1.getdata ( );
a2.getdata( );
a3.getdata( );
cout < < a1.sum;  //public data member accessed from outside the class
cout < < a2.sum;
cout < < a3.sum;
return 0;
}