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 GNU `bc' and Other Implementations
 **********************************
 
    This version of `bc' was implemented from the POSIX P1003.2/D11
 draft and contains several differences and extensions relative to the
 draft and traditional implementations.  It is not implemented in the
 traditional way using `dc'.  This version is a single process which
 parses and runs a byte code translation of the program.  There is an
 "undocumented" option (-c) that causes the program to output the byte
 code to the standard output instead of running it.  It was mainly used
 for debugging the parser and preparing the math library.
 
    A major source of differences is extensions, where a feature is
 extended to add more functionality and additions, where new features
 are added.  The following is the list of differences and extensions.
 
 LANG ENVIRONMENT
      This version does not conform to the POSIX standard in the
      processing of the LANG environment variable and all environment
      variables starting with LC_.
 
 NAMES
      Traditional and POSIX `bc' have single letter names for functions,
      variables and arrays.  They have been extended to be
      multi-character names that start with a letter and may contain
      letters, numbers and the underscore character.
 
 STRINGS
      Strings are not allowed to contain NUL characters.  POSIX says all
      characters must be included in strings.
 
 LAST
      POSIX `bc' does not have a \fBlast variable.  Some implementations
      of `bc' use the period (.) in a similar way.
 
 COMPARISONS
      POSIX `bc' allows comparisons only in the `if' statement, the
      `while' statement, and the second expression of the `for'
      statement.  Also, only one relational operation is allowed in each
      of those statements.
 
 IF STATEMENT, ELSE CLAUSE
      POSIX `bc' does not have an `else' clause.
 
 FOR STATEMENT
      POSIX `bc' requires all expressions to be present in the `for'
      statement.
 
 &&, ||, !
      POSIX `bc' does not have the logical operators.
 
 READ FUNCTION
      POSIX `bc' does not have a `read' function.
 
 PRINT STATEMENT
      POSIX `bc' does not have a `print' statement.
 
 CONTINUE STATEMENT
      POSIX `bc' does not have a continue statement.
 
 ARRAY PARAMETERS
      POSIX `bc' does not (currently) support array parameters in full.
      The POSIX grammar allows for arrays in function definitions, but
      does not provide a method to specify an array as an actual
      parameter.  (This is most likely an oversight in the grammar.)
      Traditional implementations of `bc' have only call by value array
      parameters.
 
 FUNCTION FORMAT
      POSIX `bc' requires the opening brace on the same line as the
      `define' key word and the `auto' statement on the next line.
 
 =+, =-, =*, =/, =%, =^
      POSIX `bc' does not require these "old style" assignment operators
      to be defined.  This version may allow these "old style"
      assignments.  Use the `limits' statement to see if the installed
      version supports them.  If it does support the "old style"
      assignment operators, the statement "a =- 1" will decrement `a' by
      1 instead of setting `a' to the value -1.
 
 SPACES IN NUMBERS
      Other implementations of `bc' allow spaces in numbers.  For
      example, "x=1 3" would assign the value 13 to the variable x.  The
      same statement would cause a syntax error in this version of `bc'.
 
 ERRORS AND EXECUTION
      This implementation varies from other implementations in terms of
      what code will be executed when syntax and other errors are found
      in the program.  If a syntax error is found in a function
      definition, error recovery tries to find the beginning of a
      statement and continue to parse the function.  Once a syntax error
      is found in the function, the function will not be callable and
      becomes undefined.  Syntax errors in the interactive execution
      code will invalidate the current execution block.  The execution
      block is terminated by an end of line that appears after a
      complete sequence of statements.  For example,
 
           a = 1
           b = 2
 
      has two execution blocks and
 
           { a = 1
             b = 2 }
 
      has one execution block.  Any runtime error will terminate the
      execution of the current execution block.  A runtime warning will
      not terminate the current execution block.
 
 INTERRUPTS
      During an interactive session, the SIGINT signal (usually
      generated by the control-C character from the terminal) will cause
      execution of the current execution block to be interrupted.  It
      will display a "runtime" error indicating which function was
      interrupted.  After all runtime structures have been cleaned up, a
      message will be printed to notify the user that `bc' is ready for
      more input.  All previously defined functions remain defined and
      the value of all non-auto variables are the value at the point of
      interruption.  All auto variables and function parameters are
      removed during the clean up process.  During a non-interactive
      session, the SIGINT signal will terminate the entire run of `bc'.
 

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