Basic Concepts of OOP in C++ Darvay Zsolt

C++ 2 Outline  The namespace and its members  The using declaration and directive  The address operator and the reference type  The scope operator  The type identifier operator  Comparison of simle Java and C++ codes

C++ 3 Outline  Data protection using modular programming in C  Abstract Data Types  Classes

C++ 4 The Namespace and its Members  The namespace concept  Example  Accessing the members of the namespace

C++ 5 The Namespace Concept  With a namespace one can attain the grouping of some declarations.  The names which are interconnected to each other will belong to the same namespace.  The definition of a namespace: namespace name { // declarations, definitions }

C++ 6 Example #include namespace MyVector { int *elem; int dim; void Init(int *e, int d); void FreeVect(); void SquareVect(); void Display(); } A vector namespace with integer elements

C++ 7 Accessing the Members of the Namespace  We use the scope ( :: ) operator.  Accessing: namespace_name::member.  Example: MyVector::dim = 6;  This is valid also for functions. We use the form namespace_name::function.  Simple access with the using declaration and directive.

C++ 8 The using Declaration  To access more then one time a member: using declaration  The declaration: using namespace_name::member;  Example:using MyVector::dim;  Thendim = 14; is the same as MyVector::dim = 14;.

C++ 9 The using Directive  Simple access of all members  Form: using namespace namespace_name;  Example: using namespace MyVector;  The global using directives are used for compatibility issues with older C++ versions.

C++ 10 The iostream Header File //with using directive #include using namespace std; void Print() {... cout << endl; } //without using directive #include void Print() {... std::cout << std::endl; }

C++ 11 The Init function void MyVector::Init(int *e, int d) { elem = new int[d]; dim = d; for(int i=0; i < dim; i++) elem[i] = e[i]; }

C++ 12 The FreeVect and SquareVect functions void MyVector:: FreeVect() { delete []elem; } void MyVector:: SquareVect() { for(int i = 0; i < dim; i++) elem[i] *= elem[i]; }

C++ 13 The Display function void MyVector::Display() { for(int i = 0; i < dim; i++) std::cout << elem[i] << '\t'; std::cout << std::endl; }  If the using namespace std; directive is present, then std:: can be dropped.

C++ 14 The main function int main() { int t[]={11, 22, 33, 44}; using namespace MyVector; Init(t, 4); // if there is no using, then // MyVector::Init SquareVect(); Display(); FreeVect(); }

C++ 15 The Address Operator and the Reference Type  Address operator (C and C++): & expression  where expression must be a modifiable lvalue.  In C this operator is often used when calling the scanf function.

C++ 16 Reference Type (C++)  In other words: alias name.  We use the address operator  Two variants: type & name = data;  or type & formal_parameter  type & is a new type (reference type).

C++ 17 Example (Reference Type) int main() { int x[4] = {10, 20, 30, 40}; int& y = x[0]; // y and x[0] are the same int* z = x; // *z and x[0] are the same y = 50; // y, x[0] and *z changes *z = 60; // y, x[0] and *z changes }

C++ 18 The Scope Operator  Possible forms: classname :: member namespacename :: member :: name :: qualified_name global scope

C++ 19 Global Scope  Use it to access the global variables. Example: int x = 100; int main() { char x = ’Z’; cout << x << endl; // local (character: ’Z’ ) cout << ::x << endl; // global (integer: 100) }

C++ 20 Example 2 #include using namespace std; namespace X { int x_var; namespace Y { int x_var; } double x_var = 5.25; Y: embedded namespace global variable

C++ 21 Example 2 (main function) int main() { char x_var = 'A'; X::x_var = 10; // from the X namespace X::Y::x_var = 20; // Y::x_var qualified name cout << x_var << endl; // local ('A’) cout << X::x_var << endl; // 10 cout << ::x_var << endl; // global (5.25) cout << X::Y::x_var << endl; // 20 }

C++ 22 The Type Identifier Operator  typeid operator: typeid(typename) or typeid(expression)  Returns an object, which makes possible to find out the type of an expression in running time.

C++ 23 Using the typeid Operator #include using namespace std; int main() { cout << typeid( 97 ).name() << endl; cout << typeid( 97.0 ).name() << endl; cout << typeid( 97.0f ).name() << endl; cout << typeid( 'a' ).name() << endl; cout ('a') ).name() << endl; }

C++ 24 Output int double float char int  We need the typeinfo.h header file in case of using the typeid operator.

C++ 25 Simple Code in C++ #include using namespace std; int main() { cout << "Hello" << endl; }

C++ 26 Simple Code in Java public class Hello { public static void main(String[] args) { System.out.println("Hello"); }

C++ 27 Comparison  In Java there is no include or namespace (include and import are different).  In C++ main is a function, not a method.  The list of formal parameters can be empty, if we don’t want to use them.  In C++ we use streams for input/output opertations. The << (insertion) operator can be used with the standard cout object.  In Java the name of the public class must be the same as the file name. In C++ there is no such restriction.

C++ 28 Comparison  The string literals are written in the same way, but the type of "Hello"  in C++ is const char[6]  in Java is an object of type String, and thus it is composed of unicode characters.

C++ 29 Many Similarities  Comments  Identifiers  Keywords  Literals

C++ 30 Java String and C++ string  We compare the Java String object with the C++ string “almost container”.  Differences:  Java stores unicode, and C++ ASCII characters  the Java String is immutable  in Java the concatenation (+) operator can be used for each object, but in C++ only for two strings.

C++ 31 Java String and C++ string  For a C++ string object we can use the following operators: == != =  In Javaban we use methods: equals, compareTo.  Substring: in C++ substr, and in Java substring.

C++ 32 Data Protection Using Modular Programming in C  We use static variables declared outside of functions.  One file contains all the data and the relevant code.  In the other file we can access the functions.

C++ 33 A Vector Module  Two files:  MyVector.cpp  MyMain.cpp  The two files must be in the same project.

C++ 34 MyVector.cpp #include using namespace std; static int* elem; static int dim;

C++ 35 The Init function void Init(int *e, int d) { elem = new int[d]; dim = d; for(int i=0; i < dim; i++) elem[i] = e[i]; }

C++ 36 The FreeVect and SquareVect functions void FreeVect() { delete []elem; } void SquareVect() { for(int i = 0; i < dim; i++) elem[i] *= elem[i]; }

C++ 37 The Display function void Display() { for(int i = 0; i < dim; i++) cout << elem[i] << '\t'; cout << endl; }

C++ 38 MyMain.cpp void Init(int *, int ); void FreeVect(); void SquareVect(); void Display(); //extern int * elem;

C++ 39 The main function int main() { int t[]={1, 2, 3, 4}; Init(t, 4); SquareVect(); //elem[1] = 100; Display(); FreeVect(); }

C++ 40 Abstract Data Type  A structure with data and code struct name { // data // code }; data members member functions

C++ 41 ADT  The declaration of member functions will be inside the structure, and the definition outside.  If the whole definition is inside, then the function will be inline (evaluates like a macro)

C++ 42 ADT MyVector struct MyVector { int *elem; int dim; void Init(int *e, int d); void FreeVect(); void SquareVect(); void Display(); }; data members member functions

C++ 43 Member function definitions  Definition of member functions just like in the case of namespaces.

C++ 44 The main function int main() { int t[]={1, 3, 5, 7}; MyVector v; v.Init(t, 4); v.SquareVect(); v.elem[1] = 100;// no protection v.Display(); v.FreeVect(); }

C++ 45 The MyVector class class MyVector { private: int *elem; int dim; public: MyVector(int *e, int d); ~MyVector(); void SquareVect(); void Display(); };

C++ 46 Constructor MyVector::MyVector(int *e, int d) { elem = new int[d]; dim = d; for(int i=0; i < dim; i++) elem[i] = e[i]; }

C++ 47 Destructor MyVector::~MyVector() { delete []elem; }

C++ 48 The SquareVect and Display functions void MyVector:: SquareVect() { for(int i = 0; i < dim; i++) elem[i] *= elem[i]; } void MyVector::Display() { for(int i = 0; i < dim; i++) cout << elem[i] << '\t'; cout << endl; }

C++ 49 The main function int main() { int t[]={2, 4, 6, 8}; MyVector v(t, 4); v.SquareVect(); //v.elem[1] = 100; v.Display(); }