Global Variables in Scilab

Within the Scilab environment, you're not just limited to local variables; you can also harness the power of global variables.

But first, let's demystify the term. What exactly is a global variable? Simply put, it's a variable that's accessible and modifiable from any corner of your code, irrespective of its origin—be it a specific function or a broader script. This becomes especially invaluable when you're aiming to share data across multiple functions without the hassle of passing them as arguments.

In Scilab, you can declare a variable as global using the keyword global.

global variableName

Here's a practical illustration.

Let's say you declare "x" as a global variable using the 'global' keyword.

global x

Once you've done that, this global variable "x" is at your disposal, whether you're working within a function or outside it.

For a clearer perspective, consider this example.

In the following script, while "x" wears the global hat, "y" remains local.

1. x = 1
2. y = 2
3. function myFunction()
4. global x
5. x=10
6. y=20
7. endfunction
8. myFunction()
9. disp(msprintf('x= %d', x))
10. disp(msprintf('y= %d', y))

Initially, "x" and "y" are assigned values of 1 and 2, respectively.

Inside the myFunction, "x" retains its global status, but "y" stays local.

Subsequently, we reassign the values 10 and 20 to "x" and "y".

After the function's execution, the output reads:

x=10
y=2

This underscores the fact that the local "y" value change remains confined to the function, whereas the global "x" value change reverberates outside it.

Wondering how to ascertain a variable's global status in Scilab?

The `isglobal()` function is your answer. It returns true (T) if the variable in question is global and false (F) if not.

For instance, `isglobal('x')` will confirm that "x" is indeed global, returning "T" (True).

isglobal('x')

ans=T

Conversely, `isglobal('y')` will return "F" (False), indicating "y"'s local nature.

isglobal('y')

ans=F

But here's a crucial question: When should you actually use global variables?

While global variables provide a seamless way to share data across your program, they come with a caveat. They can make your code intricate and somewhat elusive, given that their values can shift unpredictably throughout the program. This can sometimes make tracking changes akin to finding a needle in a haystack.

As a rule of thumb, it's wise to gravitate towards local variables when feasible. They not only offer tighter control but also ensure a tidier and more transparent codebase.

What's the difference between global and local variables? To wrap up, let's delineate the distinction between global and local variables. A global variable is your go-to when you need a variable accessible across the board—from functions to modules. On the flip side, a local variable remains ensconced within the function it's declared in, ensuring its accessibility is limited to that realm.