1. Concordia University Department of Computer Science and Software Engineering Click to edit Master title style ADVANCED PROGRAM DESIGN WITH C++ Part 1: Program Structure Joey Paquet, 2007-2014 1COMP 345 - Advanced Program Design with C++

2. Concordia University Department of Computer Science and Software Engineering Click to edit Master title style PROGRAM STRUCTURE free functions and main function compilation unit header file, implementation file namespaces Joey Paquet, 2007-2014 2COMP 345 - Advanced Program Design with C++

3. Concordia University Department of Computer Science and Software Engineering C++ is a superset of C Main function is the program driver Free functions Data structures A C program is a valid C++ program Classes encapsulate other functions: Object-oriented The main function is a free function, not a class member Structure of C++ programs Joey Paquet, 2007-2014 3COMP 345 - Advanced Program Design with C++

4. Concordia University Department of Computer Science and Software Engineering Simple C++ program Joey Paquet, 2007-2014 4COMP 345 - Advanced Program Design with C++

5. Concordia University Department of Computer Science and Software Engineering Only simplistic programs are self-contained into one file C++ is a language that specifies programming structures and includes only basic data structures and operators Most programs require the use of libraries Complier will compile the library’s code and the program’s code, then the linker will link them Program structure: multiple files programs Joey Paquet, 2007-2014 5COMP 345 - Advanced Program Design with C++

6. Concordia University Department of Computer Science and Software Engineering Aside from having to use libraries, large programs need to be split into different files for various reasons: Speed up compilation: Upon changes to the code, the compiler will recompile only the files that had a change. Increase organization, decrease browsing time: Physically splitting your code along logical lines will make it easier to browse through the code to locate classes, functions, etc. Facilitate code reuse: Modular physical design allows for grouping related entities and separating them from less related ones. Each group can then be logically designed to be reusable across different projects. Reused code can be fixed, fixing all projects that use it. Split coding responsibilities among programmers: For really large projects, several programmers are involved. The larger are the program files, the more likely it is that several programmers are changing the same file simultaneously. Program structure: multiple files programs Joey Paquet, 2007-2014 6COMP 345 - Advanced Program Design with C++

7. Concordia University Department of Computer Science and Software Engineering In C++, a compilation unit is a file A file may contain several functions, data structures, or classes (unlike Java) Each compilation unit is compiled individually into an object file The linker then attempts to resolve cross-references between the object files to form the unique executable file Program structure: compilation unit Joey Paquet, 2007-2014 7COMP 345 - Advanced Program Design with C++

8. Concordia University Department of Computer Science and Software Engineering Program Parts, or components Kept in separate files Compiled separately and linked together before the program runs Much more freedom to define what is a “part”, as it can be composed of a group of functions, data structures and classes In C++, there is a separation between the interface and the implementation of a component Each component is a group of highly cohesive and highly coupled elements Program structure: compilation units as program parts Joey Paquet, 2007-2014 8COMP 345 - Advanced Program Design with C++

9. Concordia University Department of Computer Science and Software Engineering Cohesion: The degree to which the elements of a module belong together in the achievement of a common goal. Cohesion is increased if: The functionalities embedded in a module have much in common. The composing elements carry out a small number of related activities, by avoiding coarsely grained and/or unrelated sets of data. Advantages of high cohesion: Increased understandability of modules (simpler, fewer operations). Increased maintainability, because changes in one module require fewer changes in other modules. Increased reusability, because application developers will find the component they need more easily among the cohesive set of operations provided by the module. Program structure: cohesion Joey Paquet, 2007-2014 9COMP 345 - Advanced Program Design with C++

10. Concordia University Department of Computer Science and Software Engineering Coupling: the degree to which an element relies on other elements for its operation Coupling is not a desired quality, but is a side-effect of defining different elements to carry a common task Much related to cohesion: good modules exhibit high cohesion and high coupling Coupling between modules is what really needs to be avoided Disadvantages of high coupling: A change in one module forces a ripple effect of changes in other modules Assembly of modules requires more effort due to the increased inter- module dependency A module might be harder to reuse and/or test because dependent modules must be included Program structure: coupling Joey Paquet, 2007-2014 10COMP 345 - Advanced Program Design with C++

11. Concordia University Department of Computer Science and Software Engineering Programs may have header files (.h ) and program files (.cpp ) No one-to-one relationship between file and classes as in Java Can have one file that contains many classes Not necessary, can have the whole program in a single file Additional “physical design” consideration Important aspect of C++ program design Program structure: header files and implementation files Joey Paquet, 2007-2014 11COMP 345 - Advanced Program Design with C++

12. Concordia University Department of Computer Science and Software Engineering Interface/header File (.h file) Contains class declaration with free functions and operators declarations Useful to programmers, as it is an abstract view of a module Separate compilation unit Implementation File (.cpp file) Contains free/member function definitions Separate compilation unit Program structure: header files and implementation files Joey Paquet, 2007-2014 12COMP 345 - Advanced Program Design with C++

13. Concordia University Department of Computer Science and Software Engineering Header files are intended for providing forward declarations to the compiler Typically, for each x.cpp file, there is a corresponding x.h file Any program file using entities defined in x.cpp will #include “x.h” This way, this program file does not use unresolved identifiers The linker will later make the proper connections on the object files In Java, this is solved by having files named after the single class they contain The Java model is much easier to use, though less flexible than the C++ model Program structure: header files Joey Paquet, 2007-2014 13COMP 345 - Advanced Program Design with C++

14. Concordia University Department of Computer Science and Software Engineering A module’s interface should always be in its header file Programs that use this module will "include" it. There is different syntax to use if you are including a user-defined module, or an existing library module: #include “mymodule.h” Quotes indicate a user-defined module The compiler will find it in your working directory #include indicate predefined library header file The compiler will find it in the library directories Using different search paths Program structure: header files Joey Paquet, 2007-2014 14COMP 345 - Advanced Program Design with C++

15. Concordia University Department of Computer Science and Software Engineering A module’s implementation code should be in.cpp file Typically give interface file and implementation file the same name mymodule.h and mymodule.cpp Not enforced, but failure to do so is confusing A module is composed of classes and free functions All the modules’ classes’ member function and free functions are defined here Implementation file must #include the module’s header file, as it contains the module’s classes and data structures declarations.cpp files contain the executable code Function definitions, including main(), free functions, member functions. Program structure: implementation files Joey Paquet, 2007-2014 15COMP 345 - Advanced Program Design with C++

16. Concordia University Department of Computer Science and Software Engineering Header file: example Joey Paquet, 2007-2014 16Advanced Program Design with C++ //This is the header file dtime.h. This is the interface for the class DigitalTime. //Values of this type are times of day. The values are input and output in //24 hour notation as in 9:30 for 9:30 AM and 14:45 for 2:45 PM. #ifndef DTIME_H #define DTIME_H #include using namespace std; class DigitalTime { public: DigitalTime(int theHour, int theMinute); DigitalTime( ); getHour( ) const; getMinute( ) const; void advance(int minutesAdded); void advance(int hoursAdded, int minutesAdded); friend bool operator ==(const DigitalTime& time1, const DigitalTime& time2); friend istream& operator >>(istream& ins, DigitalTime& theObject); friend ostream& operator <<(ostream& outs, const DigitalTime& theObject); private: int hour; int minute; static void readHour(int& theHour); static void readMinute(int& theMinute); static int digitToInt(char c); }; #endif //DTIME_H

17. Concordia University Department of Computer Science and Software Engineering Implementation file: example Joey Paquet, 2007-2014 17Advanced Program Design with C++ //This is the implementation file: dtime.cpp of the class DigitalTime. //The interface for the class DigitalTime is in the header file dtime.h. #include using namespace std; #include "dtime.h" //Uses iostream and cstdlib: DigitalTime::DigitalTime(int theHour, int theMinute) { if (theHour 24 || theMinute 59){ cout << "Illegal argument to DigitalTime constructor."; exit(1); } else{ hour = theHour; minute = theMinute; } if (hour == 24) hour = 0; } DigitalTime::DigitalTime( ){ hour = 0; minute = 0; } int DigitalTime::getHour( ) const{ return hour; } int DigitalTime::getMinute( ) const{ return minute; } // All other member functions and operators definitions declared in dtime.h should be defined here }

18. Concordia University Department of Computer Science and Software Engineering Header files are typically included multiple times e.g., class interface included by class implementation and program file Must only be compiled once else, multiply defined names No guarantee which " #include " in which file the compiler might see first Use preprocessor directives Tell compiler to include header file only once Program structure: redundant includes Joey Paquet, 2007-2014 18COMP 345 - Advanced Program Design with C++

19. Concordia University Department of Computer Science and Software Engineering Header file fname.h structure: #ifndef FNAME_H #define FNAME_H … //Content of header file … #endif FNAME typically name of file for consistency, readability This syntax avoids multiple definitions from compiling the same header file more than once May also use: #pragma once … //Content of header file … Program structure: redundant includes Joey Paquet, 2007-2014 19COMP 345 - Advanced Program Design with C++

20. Concordia University Department of Computer Science and Software Engineering In fact, this is a specialized use of the conditional compilation preprocessor directive. Conditional compilation: #ifdef x //or ifndef... #else... #endif Can be used to switch between portions of code by switching on/off x, e.g. machine-dependent code. Program structure: redundant includes Joey Paquet, 2007-2014 20COMP 345 - Advanced Program Design with C++

21. Concordia University Department of Computer Science and Software Engineering Namespace: Collection of name definitions inside of a program, potentially across different files For example, namespace “std” is common in libraries Has all standard library definitions we need #include using namespace std; Includes entire standard library of name definitions #include using std::cin; using std::cout; Can specify just the objects we want Can be more efficient, as it avoids including things we don’t use Program structure: namespaces Joey Paquet, 2007-2014 21COMP 345 - Advanced Program Design with C++

22. Concordia University Department of Computer Science and Software Engineering Used as a solution to resolve potential name clashes Large programs use many classes and functions As a program re-uses many other files, it increases the possibility of encountering entities that have the same name Namespaces are meant to deal with this A namespace can be turned "on" with the using namespace directive If names might conflict, switch it off But how to “switch it off” after it has been activated? You cannot, but conveniently, the using directive is effective only in the code block in which it is used (see next slide). Use different namespaces in separated code blocks. Though this solution has its limitations. This is one reason why the use of using NS::name directive is advocated over using namespace NS Program structure: namespaces Joey Paquet, 2007-2014 22COMP 345 - Advanced Program Design with C++

23. Concordia University Department of Computer Science and Software Engineering Given namespaces NS1 and NS2 Both have void function myFunction() defined differently If we want to use either definitions at different places in our program, we may do the following: { using namespace NS1; myFunction(); } { using namespace NS2; myFunction(); } Program structure: namespaces Joey Paquet, 2007-2014 23COMP 345 - Advanced Program Design with C++

24. Concordia University Department of Computer Science and Software Engineering All code goes in some namespace Unless specified, code belongs to the global namespace No need for using directive Global namespace always available Implied “automatic” using directive But there is no way to “turn it off” Program structure: global namespace Joey Paquet, 2007-2014 24COMP 345 - Advanced Program Design with C++

25. Concordia University Department of Computer Science and Software Engineering To create a namespace: namespace Space1 { Some_Code } Places names defined in Some_Code into namespace Space1 Can then be made available by : using namespace Name_Space_Name And any of the entities defined (e.g. NSentity) in it can be made available by: using Name_Space_Name::NSentity Program structure: creating a namespace Joey Paquet, 2007-2014 25COMP 345 - Advanced Program Design with C++

26. Concordia University Department of Computer Science and Software Engineering As seen earlier, header files and implementation files hold different parts of the definition/declaration of the entities in a module. Thus, the same namespace needs to be declared in both In the header file (declarations): namespace Space1 { void greeting(); } In the implementation file (definitions): namespace Space1 { void greeting() { cout << "Hello from namespace Space1.\n"; } } Program structure: creating a namespace across header and implementation files Joey Paquet, 2007-2014 26COMP 345 - Advanced Program Design with C++

27. Concordia University Department of Computer Science and Software Engineering Can specify where name comes from Use "qualifier" and scope-resolution operator Used if only intend one use (or few) If overused, leads to less readable code NS1::fun1(); Specifies that fun1() comes from namespace NS1 Especially useful for parameters: int getInput(std::istream inputStream); Parameter found in istream ’s std namespace Eliminates need for using directive or declaration Program structure: inline namespace qualification Joey Paquet, 2007-2014 27COMP 345 - Advanced Program Design with C++

28. Concordia University Department of Computer Science and Software Engineering Program structure: namespaces example Joey Paquet, 2007-2014 28COMP 345 - Advanced Program Design with C++

29. Concordia University Department of Computer Science and Software Engineering Program structure: namespaces example Joey Paquet, 2007-2014 29COMP 345 - Advanced Program Design with C++

30. Concordia University Department of Computer Science and Software Engineering Compilation unit defined: A file, along with all files #include d in file Every compilation unit has unnamed namespace Written same way, but with no name All names are then local to compilation unit Use unnamed namespace to keep things "local" Scope of unnamed namespace is compilation unit Not same as global namespace Global namespace: No namespace grouping at all Global scope Unnamed namespace: Has namespace grouping, just no name Local scope Program structure: unnamed namespace Joey Paquet, 2007-2014 30COMP 345 - Advanced Program Design with C++

31. Concordia University Department of Computer Science and Software Engineering #include using namespace std; namespace { const int i = 4; // these are local to the int variable;// compilation unit } const int x = 1;// this is global int main() { cout << i << x << endl; variable = 100; return 0; } Program structure: unnamed namespace example Joey Paquet, 2007-2014 31COMP 345 - Advanced Program Design with C++

32. Concordia University Department of Computer Science and Software Engineering #include using namespace std; namespace { const int i = 4; // this is local } int i = 2; // this is global int main() { cout << i << endl; // ERROR, i is ambiguous return 0; } Program structure: global vs. unnamed namespace example Joey Paquet, 2007-2014 32COMP 345 - Advanced Program Design with C++

33. Concordia University Department of Computer Science and Software Engineering Walter Savitch, Absolute C++ (Chapter 1, 11), Addison-Wesley, 2006. Bjarne Stroustrup, The C++ Programming Language (Chapters 2,6,14,15), Addison-Wesley, 2013. Y. Daniel Liang, Introduction to Programming with C++ (Chapter 2, 13). References Joey Paquet, 2007-2014 33COMP 345 - Advanced Program Design with C++