Birthday Card - Extend with If-then-else

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From the course by The University of Edinburgh

Code Yourself! An Introduction to Programming

788 ratings

The University of Edinburgh

Code Yourself! An Introduction to Programming

788 ratings

Have you ever wished you knew how to program, but had no idea where to start from? This course will teach you how to program in Scratch, an easy to use visual programming language. More importantly, it will introduce you to the fundamental principles of computing and it will help you think like a software engineer.

From the lesson

Code Gone Loopy!

In this unit you’ll keep working with control structures, you’ll find out how to use events in your programs and how to incorporate visual and sound effects in Scratch. You’ll also start thinking about the requirements and the design of your program.

Birthday Card - Butterfly Behaviour5:22

Birthday Card - Cake Behaviour 3:26

Birthday Card - Extend with If-then-else 3:42

Birthday Card - Extend with Sounds2:13

Meet the Instructors

Dr Areti Manataki
Teaching and Research Fellow
Centre for Medical Informatics
Inés Friss de Kereki
PhD
Engineering School, Universidad ORT Uruguay

Let's add more items to the card program.

It would be good to vary the butterfly's reaction to the user's age.

For instance, if the user indicates an age younger than 8,

the butterfly could say, so young and already programming?

Well, if the user is eight or older, the butterfly could simply repeat the age and

say, well done.

In both cases, the butterfly should then invite the user to blow out the candles.

How should we modify the program to incorporate this behavior?

In order to achieve this,

we'll use another control structure which we can find in the Control palette.

The one to use is the if then else block.

This structure allows us to differentiate between the steps to be carried out

depending on whether the condition is true or not.

So I'll make some space.

I'll detach the part of the code that is no longer relevant.

And I'll attach the if then else block to my stack of code.

The condition to check is located in the if part of the block.

In this case, the condition is whether the user's age, that is

the number the user provides to the butterfly's question, is lower than eight.

This is what the code for the condition looks like.

If this condition is met, then the butterfly should say, so young and

already programming?

Let's introduce the say block in the then part of our if then else structure.

If our condition is not met, the butterfly should say the user's age,

which is the answer the user provided.

And then it should say, well done.

We'll introduce the corresponding say blocks

in the else part of our selection structure.

In both cases the butterfly would finally invite the user to blow out the candles.

Now let's test our modified card to see if it works.

We'll first test it for an age lower than eight, such as six.

Good!

The butterfly reacted as expected.

Now let's try it out for an age greater than eight.

For instance, 14.

Excellent!

The butterfly's response is as desired for this age.

Now, let's have a look at this variation of our program.

Do you think that these two versions are equivalent?

These two programs are indeed equivalent, so they bring about the same behaviour.

However, the first version is more succinct and therefore,

a better approach. Instead of using the say block twice, we use it only once.

Conceptually it is also more correct.

The butterfly says blow out the candles in both cases.

So, there is no differentiation between the case where the user is younger or

older than eight.

Now, let's reflect for a moment on the process that we follow for

developing our programs.

We gradually add features and

functionality to our program, testing them and incorporating even more.

This incremental approach is very common in software engineering.

Each new software version does more than the previous one.

In the next video, we'll apply this idea to enrich our birthday card with sounds.

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