Manipulating data

Programs are often used to manage and process data. This data is either provided by the user or collected from other computer systems. In Scratch, the Operator blocks are used to manipulate numbers and text stored in variables.

Variables

Many programming languages use variables to store information. A variable can store one piece of information, either text or a number. In a game, for example, two variables might be used to store the player’s name and score.

1Make a variable To create a variable in Scratch, select Variables in the Blocks Palette and click on the Make a Variable button. Give the new variable a meaningful name, such as score, so that the code is easy to understand. Usually, variables need to be created for all sprites, which means that all sprites can see and change the variable.

Make a Variable

my variable

score

The new variable will be displayed here

2 Use blocks with your variable Use the set [variable name] block to reset the variable’s value. For example, set score to 0. The change [variable name] by block can be used to increase or decrease the value.

set score to 0 change score by 1

Strings

Programmers often call a piece of text in a program a “string”. For example, a string can be a name, an answer to a question, or an entire sentence. In Scratch, any variable can store a number or a string, and it can store different values at different times.

join apple banana

Join strings

This block can be used to join two strings. The strings are joined without a space, so the result for this example will be “applebanana”. Variable blocks can also be used in place of words typed into the block.

letter 1 of apple

Extract letters

This block extracts one letter from a string. In this example, the first letter of the string “apple” is extracted.

length of apple

Count a string

The number of characters in a string can be counted using this block. The result for the block can be viewed by clicking on it. It can also be dropped into other blocks to use in a script.

apple contains a ?

Check strings

This block checks whether the second string input is in the first one, and gives the answer as true or false. It is also possible to check for more than one letter: apple contains app?

LISTS

A list is used to store similar pieces of information, such as a list of names. In Scratch, a list can be created from the Variables section of the Blocks Palette. List positions are used for inserting and deleting items. For example, the delete 2 of [list name] block can be used to remove the second item from a list.

Numbers

Operator blocks are a core part of Scratch, and can be used for arithmetic operations, comparisons, and to pick random numbers. Some operator blocks even work with strings.

Used for addition Used for subtraction

7 + 2 7 – 2

7 * 2 7 / 2

Computers use the symbol * for multiplication Computers use the symbol / for division

pick random 1 to 10

Chooses a random number between 1 and 10

when clicked

go to x: 0 y: 0 erase all

set length of sides to

set number of sides to

Length of the shape’s sides is randomly chosen, between 10 and 100 The angle to turn is set at 360 degrees divided by the number of sides

pick random 10 to 100

pick random 3 to 8

set angle to turn to 360 / number of sides

pen down

repeat number of sides

This repeats the code to draw each side

move length of sides steps

turn angle to turn degrees

pen up move 150 steps

Moves the sprite out of the way after drawing Drop the variable blocks into hole in the Motion block

Drawing random shapes The program above draws a random shape each time the green flag is clicked. Start by making the variables length of sides, number of sides, and angle to turn. Click the green flag several times to create random art.