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Functions in C++

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A function groups a number of program statements into a unit and gives it a name. This unit can then be invoked from other parts of the program.
C++ has added many new features to functions to make them more reliable and flexible. C++ function can be overloaded to make it perform different tasks depending on the argument passed to it.
Standard C and C++ use a feature called function prototyping. With function prototyping, you must use a description of the types of arguments when declaring and defining a function. This description is the “prototype.” When the function is called, the compiler uses the prototype to ensure that the proper arguments are passed in and that the return value is treated correctly. If the programmer makes a mistake when calling the function, the compiler catches the mistake.

In a function prototype, the argument list contains the types of arguments that must be passed to the function and (optionally for the declaration) identifiers for the arguments. The order and type of the arguments must match in the declaration, definition, and function call. Here’s an example of a function prototype in a declaration:

int translate(float x, float y, float z);

You do not use the same form when declaring variables in function prototypes as you do in ordinary variable definitions. That is, you cannot say: float x, y, z. You must indicate the type of each argument. In a function declaration, the following form is also acceptable:

int translate(float, float, float);


Since the compiler doesn’t do anything but check for types when the function is called, the identifiers are only included for clarity when someone is reading the code.
In the function definition, names are required because the arguments are referenced inside the function:

int translate(float x, float y, float z)
{
x = y = z;
}

In both C and C++, the declaration func(void); means an empty argument list. The void keyword means “nothing” in this case .
                                                              Source: C++ Notes
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