Return the size of a disk in bytes.
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 Syntax

        GT_DiskSize([<ncDrive>]) --> nDiskSize

 Arguments:

      <ncDrive> is an optional parameter that is the id of the drive
      to be checked. This paramater can be either a character value
      who's first character is taken as the drive letter or a numeric
      value where 0 = Default, 1 = A:, 2 = B:, etc... If no parameter
      is passed the default drive is used.

 Returns:

      The size of the disk in bytes.

 Description:

      GT_DiskSize() can be used the find the size of a disk in bytes.

 Examples:

      // Each of the following print the size of drive C:

      ? GT_DiskSize("C:")
      ? GT_DiskSize("C")
      ? GT_DiskSize("Clipper")         // First letter is used only.
      ? GT_DiskSize(3)

      // The next two print the size of the current drive.

      ? GT_DiskSize(0)
      ? GT_DiskSize()

 Source: DISKSIZE.PRG

 Author:  Dave Pearson