computer programming modeling a passive solar home
TRANSCRIPT
Introduction to Scratch
Computer ProgrammingModeling a Passive Solar Home
Scratch is a visual computer language Uses graphical blocks to create a program
as opposed to typewritten commands. Output is primarily visual Made to be simple to use, but it contains all
the elements of a programming language
What is Scratch?
The output is displayed on a stage, which can have several different backgrounds
Sprites are characters or objects that are moved about the stage and which also can change appearance
The inputs and results of calculations are also displayed on the stage
Scripts, or programs, are used to change the background and to move or change the appearance of sprites
Overview
Characters or pictures in the animation that you can manipulate◦ Move, Glide, Shrink, Grow, Alter, appearance
The first Sprite that shows up is the Cat In the lower right hand part of the screen are
where the Sprites are loaded, created, or altered
Sprites do not have to be characters. They can also be objects that you want to change or move, such as a lamp that can be on or off or a ball moving across the screen
Sprites
The white area in the upper right that has a background and on which the sprites move.
The stage can have multiple backgrounds which can be changed by the script
Selecting Stage, just to the left of the Sprites, brings up three tabs for the stage in the center of the window: Scripts, Backgrounds and Sounds◦ Under the Background tab, you can load in pictures
that will serve as the background behind your Sprites.◦ You can paint a background, import a background that
Scratch provides (in the Backgrounds folder), or import in your own background picture
Stage
Scripts are the computer programs that govern the movement and appearance of each Sprite or Background
They are created by dragging commands from the left column into the center column
Commands are arranged in categories shown in the upper right of the window
Scripts
MotionLooksSoundPen
ControlSensingOperatorsVariables
Variables hold numeric values◦ Create them under the “variables” commands◦ Can set or change a variable using “set” and
“change” commands Operators perform calculations
◦ Addition, subtraction, multiplication◦ Operands include existing variables and numbers◦ Operators give results that are used in “set”,
“change”, “move to”, and other commands
Calculations and Values
Start – starts the script via flag, message, or clicking
Stop – stops the script or all of the scripts Loops let you repeat parts of a script Other control blocks allow a script to
change its behavior if certain conditions are met
Controlling the Program
Follow the steps below to create a program to add two numbers together.
Steps◦ Open scratch and click on the “stage” in the lower right.◦ Select backgrounds in
the middle panel, then “edit”
◦ Use the line tool to draw a “+” and a line, as one might do for addition with a pencil and paper.
◦ Move the Cat sprite out of the way (we won’t use the sprite in this example)
A Simple Calculator
Select “Variables” in the upper left Select “Make a Variable” and create three variables.
Suggested names are “number 1”, “number 2”, and “sum”. These appear on the stage.
Move them so theymake sense, withthe sum below theline and the numbersabove
Create Variables
Click on the “Script” tab in the center panel Click on “Control” button on the upper left and drag the “When
stage clicked” into the center panel Click on the “variables” button and drag the “set” block to the
center panel, just under theexisting piece. A white line will appear that will tell you when the piece is fitting correctly.
Use the small arrow in the “set” block to change the variable from “number 1” to “sum”
Write the script
Click on “Operators” in the upper left
Drag the top operator (with the plus) so that it falls into place on the “set” block where the 1 used to be
Go back to the “variable” area and drag the “number 1” and “number 2” variables into the “+” operator. The placeholders will be highlighted when the fit is correct.
Go back to the “control” area and drag the “stop script” block to theend of the script
Write the script (continued)
On the stage, double-click on the “number 1” and “number 2” variables. Both will have a small slider beneath them.
Double-click twice on the “sum” variable. It will turn into a larger number.
Use the sliders to changevalues of“number 1” and “number 2”
Single-click anywhere onthe stage and the value of “sum” will change to be the sum of the other two variables.
Run the Script
Use scratch to calculate the change in temperature in a house due to heat loss
Activity