BASIC languages generally do not require variable declaration to be programmer friendly. ScriptBasic is no exception for compatibility reasons: you can write huge programs without declaring any variable. Although this is possible this is not a good practice. Programmers can easily mistype a variable name and end up getting a new variable with undef value instead of getting compilation error. This may cost a lot of debugging time.
To help programmers avoid such a situation ScriptBasic can be asked to report any such variable as compilation error. However this also means that the programmer has to declare the global variables. To tell ScriptBasic that a certain part of the program or the whole program requires variable declaration the programmer has to issue the declaration
declare option DeclareVars
This is a directive that does not generate any code, but tells the compiler to require variable declaration. To declare global variables the program should use the command global. For example
declare option DeclareVars
global a,b,c
declares three global variables a, b and c. The directive declare option DeclareVars is effective from the line where the directive is. Any undeclared variable used before the directive can also be used without declaration after the directive as well. For example:
a = 2
declare option DeclareVars
global b,c
b = 3
c = 4
print a,b,c
print
The variable a is implicitly declared before the directive and thus it can be used even after the directive. Before the directive the global variables are implicitly declared. As no global variable is allowed to be declared more than once such an implicitly declared variable should NOT be declared in a global declaration. For example
a = 2
declare option DeclareVars
global a
generates compilation time error. Once you switched on the variable declaration requirement, you should declare each new global variable until the end of the program. This means that all included or imported files should declare all global variables if you use the directive before including or importing a file. Because this may pose some incompatibility with older code you can use the directive
declare option AutoVars
Following this line the declaration is implicit again until the end of the program or until the next declare option DeclareVars. You can switch on and off global variable declaration forcing as many times as you like. It is also not an error to switch it on if this is already on, or off it is already off. The compiler does not count however the number of on and off directives. Thus
declare option DeclareVars
declare option DeclareVars
declare option AutoVars
is just the same as
declare option DeclareVars
declare option AutoVars
or just the same as
declare option AutoVars
It is always the last declare option directive, which is in charge.
Although you can mix program segments that require and do not require global variable declaration it is recommended to issue declare option DeclareVars at the start of the program and declare all global variables.