Functions

Function prototypes:

double pow(double x, double y);
or equivalently,
double pow(double, double);

Identifiers such as x and y that occur in parameter type lists in function prototypes are not used by the compiler. Their purpose is to provide documentation to the programmer and other readers of the code.

In C, arguments to functions are always passed by value.
In C, to get the effect of call-by reference, pointers must be used.