[[CHAIN]] is used to change seamlessly from one module to another one in a program.


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* The multi-modular technique goes back to when QBasic and QuickBASIC had module size constraints. In QB64 [[CHAIN]] has been implemented so that that older code can still be compiled, though '''it is advisable to use single modules for a single project (not counting [[$INCLUDE]] libraries), for ease of sharing and also because the module size constraints no longer exist.'''


{{PageSyntax}}
: [[CHAIN]] {{Parameter|moduleName$}}

{{PageParameters}}
* {{Parameter|moduleName$}} is a variable or a literal [[STRING]] value in quotation marks with the optional EXE or BAS file name extension.


{{PageDescription}}
* CHAIN requires that both the invoking and called modules are of either .BAS or .EXE file types.
* In Windows, '''QB64''' will automatically compile a CHAIN referenced BAS file if there is no EXE file found.
* CHAIN looks for a file extension that is the same as the invoking module's extension.
* The module's filename extension is not required. To save editing at compile time just omit the extensions in the calls.
* To pass data from one module to the other use [[COMMON SHARED]]. The COMMON list should match [[Variable Types|type]]s and names.
* '''QB64 does not retain the [[SCREEN]] mode like QBasic did.''' 
* Variable data can be passed in files instead of using [[COMMON SHARED]] values. '''QB64''' uses files to pass [[COMMON]] lists.
* [[Keywords_currently_not_supported_by_QB64#Keywords_Not_Supported_in_Linux_or_MAC_OSX_versions|Not available in Linux or macOS]]'''.


{{PageExamples}}
''Example:'' CHAIN looks for same file type extension as program module (BAS or EXE).
{{CodeStart}} '' ''
 {{Cl|CHAIN}} "Level1" '' ''
{{CodeEnd}}

''Explanation:'' The file referred to is "Level1.BAS" if the program module using the call is a BAS file. If the program was compiled, it would look for "Level1.EXE".


{{PageSeeAlso}} 
* [[RUN]]
* [[COMMON]], [[COMMON SHARED]]
* [[SHARED]]


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