C++: The Complete Reference

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Your compiler may also support other extensions that help it take better advantage
of its specific environment.
All C (and C++) keywords are lowercase. Also, uppercase and lowercase are
different: else is a keyword; ELSE is not. You may not use a keyword for any other
purpose in a program--that is, you may not use it as a variable or function name.
All C programs consist of one or more functions. The only function that must be
present is called main(), which is the first function called when program execution
begins. In well-written C code, main() contains what is, in essence, an outline of what
the program does. The outline is composed of function calls. Although main() is not
a keyword, treat it as if it were. For example, don't try to use main() as the name of a
variable because you will probably confuse the compiler.
The general form of a C program is illustrated in Figure 1-1, where f1() through
fN()
represent user-defined functions.
The Library and Linking
Technically speaking, you can create a useful, functional C or C++ program that
consists solely of the statements that you actually created. However, this is quite
rare because neither C nor C++ provides any keywords that perform such things as
input/output (I/O) operations, high-level mathematical computations, or character
handling. As a result, most programs include calls to various functions contained in
the standard library.
All C++ compilers come with a standard library of functions that perform most
commonly needed tasks. Standard C++ specifies a minimal set of functions that will be
supported by all compilers. However, your compiler will probably contain many other
functions. For example, the standard library does not define any graphics functions,
but your compiler will probably include some.
The C++ standard library can be divided into two halves: the standard function
library and the class library. The standard function library is inherited from the C
language. C++ supports the entire function library defined by Standard C. Thus, all
of the standard C functions are available for use in C++ programs that you write.
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