6.4. Function Prototypes and Argument Coercion
A function prototype (also called a function declaration) tells the compiler the name of a function, the type of data it returns, the number of parameters it expects to receive, the types of those parameters and the order in which the parameters of those types are expected.
Software Engineering Observation 6.3
Function prototypes are required unless the function is defined before it is used. Use #include preprocessing directives to obtain function prototypes for the C++ Standard Library functions from the headers of the appropriate libraries (e.g., the prototype for sqrt is in header <cmath>; a ...