Introduction to Scratch

Transcription

1 Introduction to Scratch

2 Familiarising yourself with Scratch The Stage Sprites Scripts Area Sequence of Instructions Instructions and Controls

3 If a computer is a box think of a program as a man inside the box!

4 Tell me what to do and I will do it!! and programming is all about instructing the man to do what you want!

5 The man in the computer (program) thinks just like a human. If we taught the man how to have a conversation with the computer user, what would be the first thing we would tell him to do?

6 Inputs Storage Process Output Conversations start with a question. In other words the man in the computer might ask the user for some information (INPUT). Example: What is your name? The user would then type IN their name! INPUT What is your name?

7 Inputs Storage Process Output Then the man in the computer will store the answer in its brain (STORAGE) and think about how to respond (PROCESS). 1. Remember the answer (STORE IT) 2. Think about how to respond (Process)

8 Inputs Storage Process Output The man in the computer would finally respond (OUTPUT). Example: So, your name is BOB! What a great name! The computer would display this on the screen (OUTPUT). OUTPUT

9 Inputs Storage Process Output All programs work in this way Think of a word processor: INPUT STORAGE/PROCESS OUTPUT 1. Users can press a letter on a keyboard (input) 2. The computer stores this event and decide how to respond (storage/process) 3. And then display the letter on the screen (output)

10 Inputs Storage Process Output The ASK script asks the user to enter (input) a value into scratch?

11 Inputs Storage Process Output What do you get when you ask a question? ANSWER! Once you have inputted a value into scratch it is stored in a variable called answer. This is what the script looks like

12 Storage What is a variable? In programming, a variable can be thought of as a storage box. The box may be given a name, and it may hold various different things. In scratch, is the name of the variable, and it will store whatever you type into scratch. Variable called ANSWER Contents is anything we type in

13 Inputs Storage Outputs Which of the following scripts do you think will help us output a value onto the screen?

14 The Join Script We can also join words and the ANSWER together to create sentences:

15 Moving your Sprite In programming, things always happen in a set order a sequence. Sequences are first written as a flow chart and then programmed in a game. If we want to move a sprite left the following sequence would have to occur: Press right arrow key Sprite faces to the right Sprite moves a step to the right In Scratch, we program the sprite like this:

16 Inputs, Outputs, Variables and Decisions

17 Inputs Storage Process Output In Scratch, which of the following scripts will help us program the man (inside the computer) to demand an input from a user?

18 Inputs Storage Process Output The ASK script asks the user to enter (input) a value into scratch?

19 Inputs Storage Process Output What do you get when you ask a questions? ANSWER! Once you have inputted a value into scratch it is stored in a variable called answer. This is what the script looks like

20 Storage What is a variable? In programming, a variable can be thought of as a storage box. The box may be given a name, and it may hold various different things. In scratch, is the name of the variable, and it will store what ever you type into scratch. Variable called ANSWER Contents is anything we type in

21 Inputs Storage Process Output Which of the following scripts do you think will help us program the man (inside the computer) to output a value onto the screen?

22 Summary INPUT SCRIPTS: STORAGE SCRIPTS: OUTPUT SCRIPTS: The join script is a nice extra to combine set text with the user s text to form sentences when outputting to the screen

23 Inputs Storage Process Output IF statements are how programs make decisions (process data). IF this occurs, I will do this ELSE, I will do that IF ELSE statements allow programs to make decisions based on certain conditions occurring.

24 What s going on here? Program asks the user to input a number from 1 to 3 Program stores their input in the variable called answer IF answer contains 1, the program will display a message IF answer contains 2, the program will display a different message IF answer contains 3, the program will display a different message

25 Inputs, Outputs, Variables and Decisions You are all going to be real computer programmers!!!

26 Today We will create a simple calculator in scratch which will add two numbers together and display the result 2 5

27 So how can we get our sprite to do the following? Ask for a number? Store the number? Ask for another number? Store the number? First issue: Scratch only has one variable (storage box) answer. Scratch can therefore only store one number!? Display their Sum We need 2!! Number 1 Number 2

28 Storage What is a variable? In programming, a variable can be thought of as a storage box. The box may be given a name, and it may hold various different things. In scratch, is the name of a ready made variable, and it will store what ever you type into scratch. Variable called ANSWER Contents is anything we type in

29 So how can we get our sprite to do the following? Ask for a number? Store the number? Ask for another number? Store the number? Display their Sum