A friend function of a class is defined outside that class' scope but it has the
right to access all private and protected members of the class. Even though
the prototypes for friend functions appear in the class definition, friends are
not member functions.
A friend can be a function, function template, or member function, or a class
or class template, in which case the entire class and all of its members are
friends.
To declare a function as a friend of a class, precede the function prototype in
the class definition with keyword friend as follows −
Default Arguments in C++
A default argument is a value provided in function declaration that is automatically assigned by the
compiler if caller of the function doesn’t provide a value for the argument with default value.
Following is a simple C++ example to demonstrate use of default arguments. We don’t have to write 3
sum functions, only one function works by using default values for 3rd and 4th arguments.
C++ function call by reference
The call by reference method of passing arguments to a function copies
the reference of an argument into the formal parameter. Inside the function,
the reference is used to access the actual argument used in the call. This
means that changes made to the parameter affect the passed argument.
To pass the value by reference, argument reference is passed to the
functions just like any other value. So accordingly you need to declare the
function parameters as reference types as in the following function swap(),
which exchanges the values of the two integer variables pointed to by its
arguments
C++ function call by value
The call by value method of passing arguments to a function copies the
actual value of an argument into the formal parameter of the function. In
