Final answer:
The leftmost operand of a non-member operator function can be either of the operands or a different type. This allows for flexible operator overloads, where operands can be of different types, and often these functions are implemented as friends to access private members of the class.
Step-by-step explanation:
The correct option is C:
When an operator function is implemented as a non-member function in C++ programming, the leftmost operand can be c) Either of the operands or a different type. This is because non-member operator functions allow for overloading operators when the left operand is not necessarily an instance of the class that defines the operator function.
Non-member operator overloads are often used for operations that are symmetric and where it feels natural for the first operand to be of a different type than the class that provides the operator overload. For example, if you have a Complex number class and want to define an addition operator, it might be useful to allow adding both complex numbers and integers to a complex number. By defining this as a non-member operator function, the left side could be either a Complex object or an integer, providing more flexibility in usage.
It is also a very common practice to implement non-member functions as friends of the class to which they pertain so they can access the class's private and protected members. However, care should be taken as this can potentially violate the encapsulation principles of object-oriented programming.