MAITRAYEE MUKERJI Object Oriented Programming in C++

Polymorphism Poly: Multiple, Many Morphism: Forms, Behavior Polymorphism  One thing with several distinct forms or behavior  In C++ refers to way in which operators or functions can behave depending on what they are operating on:- standard data types, user defined data types, same function but with different signatures (number and type of arguments), objects belonging to base or derived classes

Polymorphism Compile Time Polymorphism  Operator Overloading  Function Overloading Run Time Polymorphism  Function Overriding Templates

Operator Overloading Operator overloading refers to giving the normal C++ operators (+, *, <=, ++ etc.) additional meaning when they are applied to user defined data types. Example: MyObject d1, d2, d3; d3 = d1 + d2; Extending C++  Using classes to create new kinds of variable  Using operator overloading to create new definitions for operators

Overloading Unary Operator Counter is a variable that counts things  Nodes, persons, file access etc. Each time an event takes place, the counter is incremented by 1 The Counter can be accessed to find the current count

// object represents a counter variable Class Counter { private: unsigned int count; public: Counter () : count (0); {} int get_count() { return count;} void inc_count() { count++; } } Constructor and Initialization to zero Since count is always positive

Main () {Counter C1; cout << “\n C1=“ << C1.getCount(); C1.inc_count (); cout << “\n C1=“ << C1.getCount(); cout << endl; return 0; } ++C1;

// object represents a counter variable Class Counter { private: unsigned int count; public: Counter () : count (0); {} int get_count() { return count;} void inc_count() {count++;} } void operator ++ () {++ count; } The keyword operator is used for overloading the ++ operator

Overloading Binary Operators Adding and Subtracting Two Complex Numbers C1 = 4 + 3i C2 = 3 + 6i CAdd = C1+C2 CSub = C1-C2

struct Complex { floatreal; floatimag; }; int main() { Complex C1, C2,C3; C1.real = 4; C1.imag = 2; C2.real = 5; C2.imag = 4; C3.real = C1.real + C2.real; C3.imag = C1.imag + C2.imag; cout << C3.real << " " << C3.imag ; C3.real = C1.real - C2.real; C3.imag = C1.imag - C2.imag; cout << C3.real << " " << C3.imag ; return 0; } Complex operator+ (const Complex &C1, const Complex &C2) {Complex C3; C3.real = C1.real + C2.real; C3.imag = C1.imag + C2.imag; return C3; } Complex operator- (const Complex &C1, const Complex &C2) {Complex C3; C3.real = C1.real - C2.real; C3.imag = C1.imag - C2.imag; return C3; } C3 = C1 + C2 C3 = C1 - C2

Function Overloading An overloaded function can perform different activities depending on the number and type of data sent to it. More than one function with the same name but  Different type of input argument  Different number of input arguments  Different number and type of input arguments

// Example: Different Type of Input Arguments #include using namespace std; void printNumber (int x) { cout << “I am printing an Integer” << x << endl; } void printNumber (float x) { cout << “I am printing a Float” << x << endl; } int main() { int a= 54; float b = ; printNumber (a); printNumber (b); }

// Different number of input arguments // Printing a line of characters void printChar(); //prints “*”, 45 times in a row void printChar(char); // prints the specified character, 45 times in a row void printChar (char, int); // prints the specified character, #times specified by user int main( ) { printChar (); printChar (‘=‘); printChar (‘+’, 15); return 0; } void printChar( ) { for (int j = 0; j<45; j++) cout << “*”; cout << endl; }

void printChar( char ch) { for (int j = 0; j<45; j++) cout << ch; cout << endl; } void printChar( char ch, int n) { for (int j = 0; j<n; j++) cout << ch; cout << endl; }

Inheritance & Polymorphism “many form” : ability of a variable to take different types In C++, applied mainly on pointer variables  S: Base Class  T: Derived Class  p: Pointer to class S -> p can point to any object belonging to any derived class T of S  a( ): Virtual function in both S and T  Function Call: p->a() invokes  S::a() if p points to object of class S  T:: a () if dynamic binding is used and p points to object type T – T is said to overide function a() from S

Example class BaseA { public: int a; void printData () { cout << "Printing Data In Base Class: " << a << endl; } void printMsg () { cout << "Printing Msg in Base Class: " << "Hello World" << endl;} }; class DerivedA : public BaseA { public: void printData (){ cout << "Printing Data In Derived Class: " << a << endl;} };

Example …contd Code Fragment 1Code Fragment 2Code Fragment 3 BaseA* pBase; pBase = new (BaseA); pBase->a = 100; pBase->printData(); pBase->printMsg(); BaseA* pBase; pBase = new (DerivedA); pBase->a = 200; pBase->printData(); pBase->printMsg(); DerivedA* pDerived pDerived = new (DerivedA); pDerived->a = 300; pDerived->printData(); pDerived->printMsg(); Printing Data In Base Class: 100 Printing Msg in Base Class: Hello World Printing Data In Base Class: 200 Printing Msg in Base Class: Hello World Printing Data In Derived Class: 300 Printing Msg in Base Class: Hello World

Example class BaseA { public: int a; virtual void printData () { cout << "Printing Data In Base Class: " << a << endl; } void printMsg () { cout << "Printing Msg in Base Class: " << "Hello World" << endl;} }; class DerivedA : public BaseA { public: virtual void printData (){ cout << "Printing Data In Derived Class: " << a << endl;} };

Example …contd Code Fragment 1Code Fragment 2Code Fragment 3 BaseA* pBase; pBase = new (BaseA); pBase->a = 100; pBase->printData(); pBase->printMsg(); BaseA* pBase; pBase = new (DerivedA); pBase->a = 200; pBase->printData(); pBase->printMsg(); DerivedA* pDerived pDerived = new (DerivedA); pDerived->a = 300; pDerived->printData(); pDerived->printMsg(); Printing Data In Base Class: 100 Printing Msg in Base Class: Hello World Printing Data In Derived Class: 200 Printing Msg in Base Class: Hello World Printing Data In Derived Class: 300 Printing Msg in Base Class: Hello World

MAITRAYEE MUKERJI Object Oriented Programming in C++: Templates

Templates Templates make it possible to use one function or class to handle many different data types Another way of implementing polymorphism  Function Template  Class Templates  Standard Template Libraries

Function Overloading - Recap Function that returns absolute values of two numbers. int abs (int n) {return (n<0) ? -n: n; } float abs (float n) {return (n<0) ? -n: n;} double abs (double n) {return (n<0) ? -n: n;} Repetitive, time-consuming, long code Error, if found, needs to be corrected in all codes

Function Template Function Template: an automatic mechanism provided by C++, to produce a generic function for an arbitrary type T. A function template provides a well-defined pattern from which a concrete function may later be formally defined or instantiated.

Function Template - Example template anyType abs (anyType n) {return (n<0) ? –n: n; } anyType abs (anyType n) {return (n<0) ? –n: n; } anyType abs (anyType n) {return (n<0) ? –n: n; } int float template parameter declaration

Instantiation C++ does not compile the template function directly. Instead, at compile time, when the compiler encounters a call to a template function, it replicates the template function and replaces the template type parameters with actual types! The function with actual types is called a function template instance.

Function Templates – example Function to find the minimum of two numbers int intMin(int a, int b) // returns the minimum of a and b { return (a < b ? a : b); } template T genMin(T a, T b) { // returns the minimum of a and b return (a < b ? a : b); }

Example..contd main () { int a = genMin (2,10); cout << a << endl; double b = genMin (4.6, 6.4); cout << b << endl; return 0; }

Function Template Template functions for swapping two values Template function for searching an array for a specific value. The function returns the array index for the value if it finds it, otherwise -1

Function Template // Swapping two numbers template void myswap (T& tmp1, T& tmp2) {T temp; temp = tmp1;tmp1 = tmp2;tmp2 = temp; return 0;}

Function Template – Array Search // searching for a value in an array Template int find(atype* array, atype value, int size) { for (int j=0; j<size; j++) if (array[j] == value) return j; return -1; }

Class Template In C++ we can have class templates also It allows us to provide one data structure declaration / data storage that can be applied to many different types. Standard Template Library uses class templates extensively.

Class Template Example class Stack {private: int st[MAX]; int top; public: Stack() { top = -1;} void push (int var); {st[++top] = var;} int pop(); {return st[top--]; } } T T T template

Class Template Example template Stack :: Stack() {top = -1} template Stack :: Push(Type var) { st[++top] = var; } template Type Stack :: Pop() { return st[top --];}

Instantiation Classes are instantiated by defining an object using the template argument Stack s1; Stack s2;

Example Class Node { public: Node(string s); private: string data; Node* previous; Node* next; };

Contd. template Class Node { public: Node(T s); private: T data; Node * previous; Node * next; };

Reference Lafore Horstmann