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OPTION BASE Statement Details
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OPTION BASE declares the default lower bound for array subscripts.
 
OPTION BASE n%
    ■ The value of n% must be either 0 or 1. The default base is 0. If the
      following statement is encountered, the default lowest value of an array
      subscript is 1:
 
        OPTION BASE 1
 
Usage Notes
    ■ The OPTION BASE statement is never required. It is used to change the
      default lower bound for array subscripts.
    ■ The OPTION BASE statement can be used only once in a module (source
      file) and can only appear in the module-level code. An OPTION BASE
      statement must be used before you can declare the dimensions for
      any arrays.
    ■ Chained programs can have an OPTION BASE statement if no arrays are
      passed in COMMON between them in a COMMON block, or if the specified
      base is identical in the chained programs. The chained-to program
      inherits the OPTION BASE value of the chaining program if OPTION BASE
      is omitted in the latter.
 
Important
    ■ The TO clause in the DIM statement provides an easier, more flexible
      way to control the range of an array's subscripts. If the lower
      bound of an array subscript is not explicitly set, OPTION BASE can be
      used to change the default lower bound to 1.