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Passing parameters

This process of providing information to a function when you call it is commonly referred to as passing parameters to the function. For the square-root function, you need to pass a parameter whose value is the value ofthe number for which you need the square root.

You call the built-in square root function in Scratch 2.0 by dragging the bottom block shown in Image B into the programming panel and selecting sqrt in the pull down list. You pass the parameter by entering a literal value or dragging a variable block into the white areathat contains the 9 character in Image B .

Returning values

A function or method will usually

  • Perform an action,
  • Send back an answer
  • Some combination of the two

Performing an action

You might think of performing an action as something like causing a Scratch sprite to move to the right and change color.

None of the Scratch 2.0 mathematical functions shown in Image C perform an action. One of the purposes of this module is to teach you how to create customblocks that do perform an action.

Sending back an answer

On the other hand, a function that is designed to calculate the square root of a number needs to be able to send the square-root value back to the programthat called the function. After all, it wouldn't be very useful if the function calculated the square root and then kept it a secret. The process of sendingback an answer is commonly referred to as returning a value .

All of the Scratch mathematical functions shown in Image C return a value.

It appears that there is no straightforward way for you to cause a custom block that you design to return a value. However, I will show you a workaroundfor that situation later.

Creating your own custom blocks

The best explanation that I have found for the mechanics of creating a custom block is contained in the document titled How Do I Use the New Blocks? on the MIT website. Go to that webpage and scroll down to the section titled Make Your Own Blocks . Follow the instructions that you find there to create your own custom blocks.

Sample programs

With that as an introduction, this section will present and explain two Scratch 2.0 programs built around custom blocks.

CustomBlockTest01

This is the simplest custom block that I could come up with that:

  • Receives an incoming parameter
  • Uses the value of that parameter to compute and return a value

This program contains the two scripts and a variable shown in Image D . These scripts are tied to the cat sprite.

Image d. program code for customblocktest01.

Missing image.
Image D. Program code for CustomBlockTest01.

A global variable

The variable named var shown on the left in Image D is a global variable. That means that it is accessible by any code in the program.

The custom block

The custom block named test is shown in the bottom script in Image D . When called, this block receives an incoming numeric parameter known locally as number1 . The code in the block multiplies that value by a factor of 2 and stores the resulting product in the variable named var , making it available to the code that called the custom block.

Questions & Answers

A golfer on a fairway is 70 m away from the green, which sits below the level of the fairway by 20 m. If the golfer hits the ball at an angle of 40° with an initial speed of 20 m/s, how close to the green does she come?
Aislinn Reply
cm
tijani
what is titration
John Reply
what is physics
Siyaka Reply
A mouse of mass 200 g falls 100 m down a vertical mine shaft and lands at the bottom with a speed of 8.0 m/s. During its fall, how much work is done on the mouse by air resistance
Jude Reply
Can you compute that for me. Ty
Jude
what is the dimension formula of energy?
David Reply
what is viscosity?
David
what is inorganic
emma Reply
what is chemistry
Youesf Reply
what is inorganic
emma
Chemistry is a branch of science that deals with the study of matter,it composition,it structure and the changes it undergoes
Adjei
please, I'm a physics student and I need help in physics
Adjanou
chemistry could also be understood like the sexual attraction/repulsion of the male and female elements. the reaction varies depending on the energy differences of each given gender. + masculine -female.
Pedro
A ball is thrown straight up.it passes a 2.0m high window 7.50 m off the ground on it path up and takes 1.30 s to go past the window.what was the ball initial velocity
Krampah Reply
2. A sled plus passenger with total mass 50 kg is pulled 20 m across the snow (0.20) at constant velocity by a force directed 25° above the horizontal. Calculate (a) the work of the applied force, (b) the work of friction, and (c) the total work.
Sahid Reply
you have been hired as an espert witness in a court case involving an automobile accident. the accident involved car A of mass 1500kg which crashed into stationary car B of mass 1100kg. the driver of car A applied his brakes 15 m before he skidded and crashed into car B. after the collision, car A s
Samuel Reply
can someone explain to me, an ignorant high school student, why the trend of the graph doesn't follow the fact that the higher frequency a sound wave is, the more power it is, hence, making me think the phons output would follow this general trend?
Joseph Reply
Nevermind i just realied that the graph is the phons output for a person with normal hearing and not just the phons output of the sound waves power, I should read the entire thing next time
Joseph
Follow up question, does anyone know where I can find a graph that accuretly depicts the actual relative "power" output of sound over its frequency instead of just humans hearing
Joseph
"Generation of electrical energy from sound energy | IEEE Conference Publication | IEEE Xplore" ***ieeexplore.ieee.org/document/7150687?reload=true
Ryan
what's motion
Maurice Reply
what are the types of wave
Maurice
answer
Magreth
progressive wave
Magreth
hello friend how are you
Muhammad Reply
fine, how about you?
Mohammed
hi
Mujahid
A string is 3.00 m long with a mass of 5.00 g. The string is held taut with a tension of 500.00 N applied to the string. A pulse is sent down the string. How long does it take the pulse to travel the 3.00 m of the string?
yasuo Reply
Who can show me the full solution in this problem?
Reofrir Reply
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Source:  OpenStax, Teaching beginners to code. OpenStax CNX. May 27, 2013 Download for free at http://cnx.org/content/col11498/1.20
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