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In this video, we'll learn a little bit more about classes and objects.

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You can think of classes as blueprints from which objects are created.

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Classes are user-defined types.

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And one of the goals in object-oriented programming

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is to make the user-defined types feel like they're part of the programming language.

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So when we create our classes,

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we want to be able to use them, just like we use integers, doubles and so forth,

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easy and simple.

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Classes have attributes which are data.

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And they also have functions, which are called methods.

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As mentioned in the previous videos,

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classes can hide data and methods that are only used internally by the class.

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This is done using the private and public access modifiers.

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The goal of a class is to provide a well-defined public interface

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that the user of the class can easily use to solve their problem.

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Here are some example classes:

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account, employee, image, standard vector and standard string.

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These are all classes that model real-world entities.

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Vector and string are part of the c++ standard library.

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Account, employee and image might be classes that we would create in our applications.

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Okay. So now that we know what a class is, what's an object?

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Well, objects are created from classes and represent a specific

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instance of the class they're created from.

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So if I have an account class, I can create a Frank's account object

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that's a specific instance of an account that models Frank's account information.

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We can have as many objects as we need.

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If we were modeling a real banking application,

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we could have hundreds of thousands of account objects,

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each representing an individual instance of an account.

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Each object has its own identity,

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and each can use the methods defined in the class.

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Let's see an example.

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We know that ints and doubles are primitive types in c++.

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They're not classes, but this analogy will help make a point.

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In the first two lines, we define two integers, high score and low score.

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What does that tell us? Well, it tells us what the valid values are for those variables,

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and it also tells us the operations we can perform on those variables,

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for example, addition, subtraction, multiplication and so forth.

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Again, integers are not classes.

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But just for a moment, think of int as the class

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and low score and high score as objects created from the int class.

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Notice that low score and high score are instances of integer.

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They each have a value, and they each have an identity.

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Now look at the next two lines.

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Let's assume that we've already written the account class, and it's a true c++ class.

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Notice the syntax and how similar it is to the syntax for the integers above.

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Account is a user-defined type.

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So Frank account and Jim account are instances of the account class,

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they are objects.

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Each of these objects has an identity and values associated with them,

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just like high and low score did.

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This should look familiar since we've already been using objects all along.

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The last two lines create a scores object

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that's an instance of a vector of integers

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and a name object that's an instance of string.

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Okay. So now that we know a little bit more about classes and objects,

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let's see how we can declare a class in c++ in the next video.