BJC U2L1 Global vs. Local Variables

What will the script say?

• 50, 50, 50

• 50, 60, 60

• 50, 60, 50

• 60, 60, 50

Answer explanation

The custom block (procedure) creates a script variable, which is temporary & exists only for the duration of that block. The script variable is erased from existence when the block finishes.

A local variable is

• a variable that is limited in scope

• is the same as a constant

• can be accessed anywhere in the program

• is the same as a block

Answer explanation

A scope may be a custom block, a script, or the whole program (all scripts & sprites).

A local variable may be a parameter (local to inside the block) or a script variable (local to the connected blocks in that script).

A predicate block will return...

• a value of any type

• nothing

• true or false

• a condition

Answer explanation

Boolean values true/false are NOT the words true/false. They're their own data type (cf. number, text, sound, etc.).

Assuming age is a global variable, what will the script say?

• 50, 60, 50

• 50, 50, 50

• 50, 60, 60

• 50, 50, 60

Answer explanation

There's only one copy of the variable age throughout the entire run of the program.

A global variable is

• accessible inside only one block in a program

• accessible by only one sprite in a program

• used as an input parameter

• accessible anywhere within the program

"i" and "branches" are not global variables. What will the script do at "say i for 3 seconds"?

• 100 for 3 seconds

• error

• say 8 for 3 seconds

• say 9 for 3 seconds

Answer explanation

branches is a parameter, a local variable within the scope of the "draw a pinwheel" procedure. It does not exist outside the block.

"a" is not a global variable. I will execute script 1. What happens when I execute script 2?

• ... 3

• ... 5

• error

• Nothing - need a hat block first

Answer explanation

a is a local variable within the scope of the script (connected blocks). It doesn't exist in the second script.

I click on script 1. "a" is a global variable set to 5.

I click on script 2.

What happens if I click on script 3?

• 3

• 5

• error

• nothing

Answer explanation

Local variables "shadow" global variables of the same name (bad practice!). So, in script 2, we're working with the local script variable a. But everywhere else, we only know the global variable a, created in the Variables palette.

x is a global variable. What will the script say?

• error

• nothing - x is undefined

• x is 5

• x is 10

Answer explanation

The custom block creates a parameter, local variable x, initialized to the argument, 5. This x disappears when the block finishes.

Outside the block, we only see the global variable x.

x is a global variable. What will script 1 say?

• x is 5

• x is 10

• x is 15

• error

Answer explanation

There's only one x, and we "say" it before the last set.