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 a large program is to construct it from small, simple pieces, or components. This technique is called divide and conquer. We introduced functions (as program pieces) in Chapter 3. In this chapter, we study functions in more depth. We emphasize how to declare and use functions to facilitate the design, implementation, operation and maintenance of large programs.
We will overview a portion of the C++ Standard Library's math functions, showing several that require more than one parameter. Next, you will learn how to declare a function with more than one parameter. We will also present additional information about function prototypes and how the compiler uses them to convert the type of an argument in a function call to the type specified in a function's parameter list, if necessary.
Next, we'll take a brief diversion into simulation techniques with random number generation and develop a version of the casino dice game called craps that uses most of the programming techniques you have learned to this point in the book.
We then present C++'s storage classes and scope rules. These determine the period during which an object exists in memory and where its identifier can be referenced in a program. You will also learn how C++ is able to keep 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 two topics that help improve program performanceinline 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 by programmers to implement functions that perform similar tasks for arguments of different types or possibly for different numbers of arguments. We consider function templatesa mechanism for 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 that is discussed at length in upper-level computer science courses.