In this chapter, we take a deeper look at functions. Most computer programs that solve real-world problems are much larger than the programs presented in the first few chapters of this book. Experience has shown that the best way to develop and maintain large programs is to construct them from small, simple pieces, or components. This technique is called divide and conquer.

We’ll overview a portion of the C++ Standard Library’s math functions. We’ll introduce function prototypes and discuss how the compiler uses them, if necessary, to convert the type of an argument in a function call to the type specified in a function’s parameter list.

Next, we’ll take a brief diversion into simulation techniques with random number generation and develop a version of a popular casino dice game that uses most of the programming techniques you’ve learned.

We then present C++’s scope rules, which determine where identifiers can be referenced in a program. You’ll learn how C++ keeps track of which function is currently executing, how parameters and other local variables of functions are maintained in memory and how a function knows where to return after it completes execution. We discuss topics that help improve program performance—inline functions that can eliminate the overhead of a function call and reference parameters that can be used to pass large data items to functions efficiently.

Many of the applications you develop will have more than one function of the same name. This technique, called function overloading, is used to implement functions that perform similar tasks for arguments of different types or different numbers of arguments. We consider function templates—a mechanism for concisely defining a family of overloaded functions. The chapter concludes with a discussion of functions that call themselves, either directly, or indirectly (through another function)—a topic called recursion.