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Hey, welcome to day 42 of the course.

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You're doing great.

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Today, we're going to learn something very important, which I haven't seen in other online courses,

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and that is extending your programs because an app, a program is like a living thing.

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It grows with time.

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In other words, you build a program, but then new ideas come, new requests from users.

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So then you might want to add more features to the program.

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And when that program is built in P style, that is a good thing because it's very easy to add more

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features to that program, to extend that program.

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So today what we're going to do is we're going to add a credit card feature to our hotel reservation

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program.

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So currently our program allows the user to book a hotel.

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Using the book method, and then the user gets a reservation ticket generated in the command line.

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So there is no payment layer in this app.

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Therefore, to satisfy our users and our clients requests, we want to make this program able to check

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a credit card.

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In other words, we want to validate a credit card in our program that will be a fake credit card.

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But the idea is the same.

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So with that in mind, I'll see you in the next video.

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Let's begin.