C Library Functions  - expression (3)

NAME
expression(3f) - [M_calculator] return value from a string expression processing messages to simplify call to CALCULATOR(3f) (LICENSE:PD)

CONTENTS

Synopsis
Description
Dependencies
Examples
See Also
Author
License

SYNOPSIS
subroutine expression(inlin0,outval,outlin0,ierr,ilen) 

    character(len=*), intent=(in)  :: inlin0
    doubleprecision, intent=(out)  :: outval
    character(len=*), intent=(out) :: outlin0
    integer, intent=(out)          :: ierr
    integer, intent=(out)          :: ilen

DESCRIPTION
expression() takes a string containing a FORTRAN-like expression and evaluates it and returns a numeric or string value as appropriate. The main purpose of expression() is to assume the burden of displaying the calculator messages for codes that make multiple calls to CALCULATOR(3f). CALCULATOR(3f) does not display error messages directly.
o EXPRESSION(3f) calls the calculator routine CALCULATOR(3f) to evaluate the expressions.
o Messages beginning with a # are considered comments and are not passed on to the calculator.
inlin0 INLIN0 is a string containing a numeric expression. The expression can be up to (iclen_calc=512) characters long. The syntax of an expression is as described in the main document of the Calc library. For example: 
              ’A=sin(3.1416/5)’
              ’# this is a comment’
              ’$STR("The value is ",40/3)’
outval OUTVAL is a numeric value calculated from the expression in INLIN0 (when IERR returns 0). When a string value is returned (IERR=2) then OUTVAL is the length of the output string.
outlin0
  OUTLIN0 contains a string representation of the number returned in OUTVAL up to 23 characters long when INLIN0 is a numeric expression. It contains a string up to (iclen_calc=512) characters long when INLIN0 is a string expression.
ierr IERR returns
o -1 if an error occurred
o 0 if a numeric value is returned (value is in OUTVAL, string representation of the value is in OUTLIN2).
o 1 if no value was returned but a message was displayed (If a ’dump’ or ’funcs’ command was passed to the calculator).
o 2 if the expression evaluated to a string value instead of a numeric value (value is in OUTLIN0).
ilen ILEN returns the length of the input string minus trailing blanks.

DEPENDENCIES
o User-supplied routines: All programs that call the calculator routine can supply their own substitute_subroutine(3f) and substitute_C(3f) procedures. See the example program for samples.

EXAMPLES
Sample program: 

    program demo_expression
    use M_calculator, only : iclen_calc
    use M_calculator, only : expression
    implicit none
    character(len=iclen_calc) :: outlin0
    doubleprecision           :: outval
    integer                   :: ierr, ilen
       call expression(’A=3.4**5    ’,outval,outlin0,ierr,ilen)
       write(*,*)’value of expression is ’,outval
       write(*,*)’string representation of value is ’,trim(outlin0)
       write(*,*)’error flag value is ’,ierr
       write(*,*)’length of expression is ’,ilen
    end program demo_expression
Results: 

    value of expression is    454.35424000000000
    string representation of value is 454.35424
    error flag value is            0
    length of expression is            8

SEE ALSO
See also: STRGAR(),RNUM0(),CALCULATOR(),INUM0(),SNUM0()

AUTHOR
John S. Urban

LICENSE
Public Domain

Nemo Release 3.1 expression (3) June 29, 2025
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