Lecture 6- Classes and Objects in C++

[Music] [Music] so welcome to lecture six classes and objects so we briefly Define how we can create the classes in C++ all right so we have also studied it is nothing but the blueprints for creating objects all right so once you create a class right assume that you're creating a class so it uh encapsulates the data all right so in fact data that means attributes and the behavior which is called functions or methods all right so in a set notation all right so we can Define this as a tuple all right so here it is nothing but a tuple C is equal to a comma M where a we call it as a set of attributes suppose you are using the data right you call it as a member data and M is nothing but a member function or you call it as methods so we have already talked about how the syntax Works in C++ so when I define a class right so here you go you will write the keyword called class right so we'll have a class keyword and then the name of the class you are opening the braces the code block is starting over here and you have the member data called attributes and you will have the functions you can have several attributes you can use arrays also all right and you can have several methods several functions right you call it as a member data or member variable or member function and then you will have the end parenthesis with a semicolon in the case of C++ you should have the semicolon this is how we can define a class in C++ so what is the motivation behind all right for class design in C++ so when we are writing objectoriented programming so as we had seen it is mainly based on the objects and classes right which is a very powerful Paradigm all right so this can solve the wide variety of problems so you can have the list of problems over here so the list of problems when you are having a class you can have a object right so class and from the class you can create the object and we can use some of the objectoriented programming Concepts like uh inheritance polymorphism encapsulation Etc right so all these can be effectively applied right we can apply so now we had seen right in the few classes back we had seen the tangible objects and intangible objects so for example right so intangible objects assume that I want to create a class or I have to solve the problem using objectoriented programming for Library Management Systems so when you have Library Management Systems you can think of right books users all right loans staff members right so these you are model mean you are modeling these as classes right you're modeling these as classes like then we have attributes for example book title all right due dates and behavior like borrowing or returning the books all right so the attributes I Define book title you call it as a member data then we can have what are all the due dates and then I if I want to write certain functions like uh borrowing or returning the books right so this is how I can think of the blueprint for the library management system similarly banking system all right so classes can represent uh customers accounts transactions all right your method can include the deposit withdrawal and balance in query so when the intangible objects like banking systems so how I can have a class so from the class right I mean I can uh represent the customers account and transactions and then I will have set of member functions all right so like uh deposit withdrawal balance inquiry Etc right so this is how I mean I can think of writing a object object oriented code for these kind of problems similarly suppose you are interested in let us say gaming the is game all right so I can think of classes for pieces like Pawn King Rook Queen right so because they have a specific movements and behaviors all right and also I can think of the board right the board can be an object so that can have all the pieces so when you're writing any games right the chess is one of the games so if you want to have right uh other board games or any other games you can think of in object oriented way similarly traffic simulations all right so we can think of vehicles roads traffic lights so these can be objects right so when I'm talking about the classes of this problem all right so the classes can Define the behavior of every component right of this traffic simulation right and the method simulate movement and traffic flow right so when I'm thinking about uh traffic simulation so I can write a program using objectoriented programming similarly when you are going for the data structures like a link list Stacks cues and trees all right so once you are done with letter say C++ and Java you can think of next one is a data structure and advanced data structure so I can define a class node right class link list class tack class cues class binary search trees class aval trees right so these are all nothing but the classes and you can have right several methods insertion right or addition of the node removal of the node or I want to manipulate certain data so these are all coming under the methods right so you can think of whenever I have a link list or any data structure so the data structure can be a class and then the several operations you can have several operations those operations are nothing but the methods or member functions right similarly we are in the artificial intelligence Paradigm right in neural networks we can use objectoriented programming like uh layers neurons the connections right so these are all can be considered as a classes and then when I'm talking about the methods you have a forward propagation backward propagation and you are to train the model correct so when I want to have objectoriented Concept in neural network so you can think of so the main idea of all these problems that I have suggested all right so you have a class so from the class you can have the objects right so once you have the objects let us assume inside the class you can have set of member data you can use any data it may be integer or double or float or even array of integers all right you can think of these are all the member data and several member functions right when I'm talking about the data structure I have to write a method for insertion deletion update pop operation in Stacks peep operation in stack push operation in stack so all these operations when I'm talking about the operations they are nothing but the methods okay so this is how I can think of using the object oriented programming how I can solve these kind of problems so similar to class design in C++ so we have class design in Java all right so when we talk about the class design in Java so here you go all right so you have name of the class so here you have name of the class right the class name and then you have attributes and methods right attributes is nothing but data member so in Java you call it as data member and then you can have set of methods and methods are nothing but the behaviors or operations or the functions that you are calling in C++ you call this in Java so the class is a keyword and you can have a name of the class you can have a attribute you can have a method so only thing after Braes you should not have a semicolon okay so this is how we can Define the class in Java so now you know how to create a class how to define a object right or how to declare a object or I can say that how to instantiate an objects right instantiate an object or instantiate the objects right so this you know that so with this we will see some of the problems okay so now write a C++ program to multiply two complex numbers using class and objects all right so you have to multiply two complex numbers so how do you define a complex number so C is equal to let us say one let us say C1 A1 + ib1 so this is one complex number and C2 equal to A2 + I B2 right when I multiply C1 into C2 it is nothing but A1 + I B1 multiplied by A2 + I B2 correct so which is nothing but A1 into A2 i s is minus1 therefore I'll get minus B1 into B2 correct plus I into B1 A2 plus A1 B2 or I can write B2 A1 all right so the multiplication when I am doing the product right so I have to get this as the output all right so these two numbers will be the input so it is a pair the pair will be the input and the program has to multiply these two complex numbers and I have to get the output like this so now the user will give you the numbers A1 B1 the pair A2 B2 the pair and the resultant I have to get this right so how we are going to solve this using object oriented programming so let us consider this program all right so let us have the class complex right I'm creating a class complex the idea is we have to multiply these two complex numbers right I'm creating a complex class complex so when I write c equal to A+ I right this a is a real value and B here is I into B we can call it as a complex imaginary value right it's a imaginary value so therefore we have float real and Float imaginary is a member data so you have two member data the member data are float real and Float imaginary next you have set of member functions all right you have member function called set values usually we see this getter and Setter function so set values so you have two parameters float R and Float I all right so whatever you are setting the value or taking the value from the user real and imaginary all right so here R will be assigned to real and I will be assigned to imaginary right sooner or later we'll talk about the access modifiers the private and public all right so right now still it is a keyword I have not explain so we will once we talk about we'll again see the complete program so right now no need to worry about the private and public so that is the reason here R will be assigned to real and I will be assigned to imaginary right so I can access this inside the class that is the meaning so when I taking the input from the user right R and I so B based on this function so when I'm passing these values in the main so now R and I you will have the value so that will be assigned to real and imaginary so this is one function and then you have another function called multiply all right so here we use the keyword static I'll explain about static maybe we'll see one or two examples all right how we are defining the keyword static all right so now complex multiply right so here you have the multiply function whose return type is the right the return type is the object right your return type is the class complex all right your return type is class complex so I will take complex address C1 and another one is complex address C2 all right so suppose I have if you would have done the reference operator int address C1 all right assume that I have int let us say C2 equal to 10 right so when I write int C2 equal to 10 so we know that let us say this will be stored in some address assume that the address is having let us assume this is your memory location all right so this is C2 taking the value 10 all right so now if I put in address C1 which is equal to C2 right so now if you look what is address of C2 address of C2 is 42 address of C2 is 42 correct so now when I write like this int address C1 equal to C2 the meaning is address C1 is also pointing to the location 42 all right so that is the meaning of this because we are using this syntax over here all right so maybe uh the syntax go like this complex when we are calling the function so you will give like this some let us say C11 all right so the meaning is address C1 and address C11 both are same right when you're are doing like this address C1 and address C11 both are same address of C1 and address of C11 both are same all right so with this in mind we'll again come back when we are calling this particular function in line number 17 all right so this concept will be useful to you so now as we uh worked out right how to multiply two complex numbers right maybe one more time I'll do it A1 + ib1 because here we have set of Expressions right into A2 + ib2 so we know that it is A1 A2 minus B1 B2 I squ is min-1 right this will be your real + I into A1 B2 + A2 B1 right so now now if you look this is a resultant right the resultant complex number let us say C3 so C3 will be it will be like a plus IB form right C3 will be some X Plus iy form right what is X that is real so X will be let us say C3 is equal to x + i y all right in that case X is equal to A1 A2 minus B1 B2 and Y is equal to A1 B2 + A2 B1 right so this you call it as result. real X is nothing but your result do real so you can see that C1 do real into C2 do real which is nothing but A1 into A2 all right and then you have minus you have minus B1 into B2 C1 do imaginary into C2 do imaginary B1 B2 and imaginary C1 do real A1 into C2 do imaginary B2 right similarly C1 do imaginary into C2 do real all right so that you have evaluated this and then return result all right so result is a complex number you can see the return type is complex right so this is one main function so you are another member function over here and the last member function is you are displaying all right you are displaying real and imaginary all right so if imaginary is greater than or equal to zero you display a plus IB otherwise a minus IB so that is the reason that's why it's been taken like this right so basically you are displaying A+ IB or X Plus iy form okay so up to here we have return the class correct so this is how we Define the class called complex so you have real and imaginary data members or member data and then you have member functions called set values multiply and then display so now come to the main program so in the main program we are creating two objects C1 and C2 and then you need another object called result right so you obviously require result is equal to C1 star C2 where C1 C2 are the complex number so result the third object all right so now you will have C1 is nothing but A1 Plus ib1 so you need real one and imaginary one and C2 is A2 plus ib2 so real 2 and imaginary 2 so take the input from the user for for example I write 2 + 3 I and then another one is 4 + 5 I all right in that case I have to write C in real one C in imaginary one all right and then you will have C1 do set value so now you are calling the object C1 you have already defined over here so the object C1 is invoking the member function the member function called set values using the dot operator so you have the object the object is invoking using dot operator and one of the member function called set values right you are pausing real one and imaginary one right you are pausing real one and imaginary one so let us say what is happening in the set values right so here you have set values assume that I'm passing two and three all right so your real is two and imaginary will be three right for the object C1 your real is two and imaginary is three so this is a meaning and then similarly C2 is invoking right you taking two more input real two and imaginary 2 right so this is your real two this is your imaginary 2 all right so now C2 is invoking set values member function right you have a DOT operator and then you are pausing real two and imaginary 2 assume that I'm pausing four and five correct so when I'm passing four and five so what I will get my R real will be four imagine will be five right C2 do real will be four C2 do imaginary will be five so this is the meaning all right so finally all right so here under the class complex all right you have scope resolution operator all right and then you are having multiply C1 comma C2 so this means I can write this function outside the class all right so when I'm writing this correct in the main all right so I can do that so that means I am calling this particular function multiply all right I'm calling this function multiply correct with passing two arguments C1 and C2 all right so when I'm calling multiply let us see what is happening so here you go multiply so complex address C1 which is equal to C1 C1 that you're passing from here right C1 do real C1 do imaginary similarly complex C2 which is equal to C2 all right so that means address C1 and add C2 so here your C1 over here right you have an object C1 in the main all right so you have object C1 in the main object C2 is also in the main correct so which is you are creating an object with some address value right so for example I create C1 whose address is let us say 42 address of C1 and I create C2 whose address is 46 so once I have this when I'm calling this your address see 1 equal to C1 so that means C1 when I Define inside the function C2 I Define inside the function both will have the same address what you have defined outside the class that is the meaning okay so now rest is fine see1 C2 you pass that means C1 real C2 imaginary C1 imaginary right and C2 real all you have passed and then this computation will be done so once this computation will be done we know know that right so the complex multiplication is happening and then you are displaying the result so you're getting a result all right your result is the object whose class is complex right so therefore you have a complex class this is called scope resolution operator and then you're calling the multiply function by pausing two arguments C1 and C2 right right so multiplication will be done when you're calling this function and result is invoking so result of multiplication this is invoking display all right so that means result do real and result do imaginary will be displayed right so this is what exactly happening all right so result do real and result do imaginary will be displayed for example assume that we are giving 2 three right 2 + 3 I the same right 2 + 3 3 I as a one input and another input is 4 + 5 I correct so when I multiply these 2 what I will get so I should get - 7 + 22 I this is obvious right 2 into 4 is 8 3 into 5 is 15 I 2 - 15 + I into 3 into 4 is 12 and 5 into 2 is 10 so 8 - 15 is - 7 + 12 + 10 is 22 I so I should get this is output in fact so this is giving the correct output right so this is how we are doing the complex multiplication using class and objects all right so what exactly we have done so we have created a class right so the class is a complex the name of the class is complex and then you have member data so real and imaginary or member data and then you have set of member functions called set values all right and then you have multiply this is a main function right main member function called multiplication and then displaying all right so you can display maybe the number one C1 complex one A1 Plus ib1 complex 2 A2 plus ib2 so this you can display all right and then result so once you are doing the complex multiplication all right so once you're doing a complex multiplication so the resultant can also be displayed using this so that means whenever you are creating an object you have member data and member function so here we have used two member data and then three member functions so up to here line number 31 you have class so once you have a class when you go to the main program you are creating objects all right so C1 C2 result these are all the objects so you know how to create a class and now you are instantiating an object or instantiating objects so the objects are nothing but C1 C2 and result right so you have the complex class and then the usual float real one imaginary one real two imaginary 2 right so usual data type so that you have used in your procedural oriented programming all right so then you're taking the input from the user so when you're taking an input from the user the set values will set all right where C1 is invoking set value C2 is invoking set value and it is nothing but you have a1+ ib1 and A2 plus ib2 and then you are calling the multiplication function so here I am using the reference operator so the reference operator C1 when you define the object in the main C1 you are defining object inside the class so both are pointing out the same location all right so this is how we have seen the concept of that integer right integer address a or integer address C1 equal to some C11 so both C1 and C11 pointing to the same address correct and then when it is uh multiply is invoking right in fact the multiply when you are calling this function with the C1 and C2 passing the arguments so these two will be multiply C1 and C2 will be multiply and the resultant will be over here right you're calling the multiplication member function so it will throw the result so result is of the form X x + i y complex number so that we are displaying so we have given the sample test 2 + 3 I and 4 + 5i so and then we got the exact output all right so this is how we can have a class and then create an object and uh you can solve as I said several problems this is one of the mathematical problems right similarly you can think of right the banking system in fact you can think of neural networks or or we will go right how to solve the problems like data structures right create a class let us say link list or even the arrays all right so create a class arrays and then you can do set of operations like uh insertion in arrays deletion in arrays updating the arrays or you can write the program like a searching you can write a function like searching member function like searching sorting all right so the main idea is so with the help of object oriented programming right so you all might have studied procedural oriented programming you can think of right so creating a class right defining a class and creating an object and then all right so you can invoke many functions all right so here we had seen several keywords right so one of the keywords you are seeing over here we'll talk about private and public slightly later and here static all right so in the next class we'll see few examples about static all right and then right how the static Works without static variable or with static variable how the results are being changed so that we will see in the next class thank you a [Music]