A C plus plus program is a collection of one or more what?

Answer 1

A C plus plus program is a collection of one or more translation units. Every C++ program requires at least one translation unit that defines the global main function, the entry point of the application. Typically, the global main function is used to parse any command line switches and delegate primary operations to one or more lower-level functions.

A translation unit is the smallest unit that can be processed by the C++ compiler. During compilation, only those units that have changed since the previous compilation need be recompiled. A unit is essentially a source file (typically a *.cpp file) and source files are typically divided up by the classes and/or functions they define, thus allowing programmers to create self-contained code modules that can used by other applications. Typically, a source file has a corresponding header file (typically a *.h file) which must be included by the source file (using the #include precompiler directive). The header typically describes the translation unit's interface and may be included in other translation units that require access to that interface.

A class is a user-defined type, in much the same way that an int or float is a built-in type. The class definition describes the type's representation and interface; the operations that are valid for the type. Class interfaces are typically defined in header files and implemented in source files. However, class templates need to be completely defined in the header as these are used by the compiler to generate types at the point of instantiation and the compiler needs to "see" the complete template definition in advance of any usage of that template.