CIS 101: Computer Programming and Problem Solving

Lecture11Usman Roshan

Department of Computer Science

NJIT

Classes

Let’s say we want to define a rectangle object. This is the same defining a new type of variable called rectangle. Previous types we have seen so far are int, char, float, and their pointers.

int length;int width;int area();float diagonal();

This is our rectangle class.it contains the length andwidth, and also functionsto compute the area anddiagonal.

Rectangle

Defining classes

class <class name> {

public:

<type> <variable of function>;

…

private:

…

};

Rectangle class

Rectangle class

Constructors, destructors, andcopy constructor

• Constructor: get called when a new instance of the object is created.– rectangle myrec; //constructor gets called

• Destructor: gets called when you exit the scope of the variable– void myfunction(){

• rectangle myrec;• myrec.setlength(2); myrec.setwidth(1); myrec.print();

– } //once we exit this function the destructor gets called• Copy constructor: gets called everytime a copy of the object is

created– rectangle myrec2 = myrec;//not called in this case, we’ll have to write

a //separate function for this which (if time) we may see later– void myfunction(rectangle myrec);– void main(){

• rectangle myrec;• myfunction(myrec) //at this point a copy of myrec is created that is local to

//myfunction– }

Constructor

Everytime we create a rectangleits length and width are automaticallyset to 2 and 2.

Overloading constructor

You can have two or more constructors:convert and default

Also called function overloading

Copy constructor

Implicit copy constructor is calledwhich copies width and length ofr1 into width and length of r2.

String class

Strings

mystring

p

size 7

string(int s){ size = s; p = new char[size]; }

string mystring(7);

string( string& from) { size = from.size; p = from.p; }

string mystring2(mystring);

mystring2

p

size 7

Strings

mystring

p

size 7

string(int s){ size = s; p = new char[size]; }

string mystring(7);

string( string& from) { size = from.size;p = new char[size]; for(int i=0;i<size;i++){

p[i]=from.p[i];}

}

string mystring2(mystring);

mystring2

p

size 7

Lab problems

1. Create string class and add functions:1. Copy string2. Compare string for equality3. Concatenate strings4. Substring

2. Create Vector class1. Copy vector2. Vector equality3. Dot product4. Euclidean norm (length) of vector