modified: diffout.py

[GalaxyCodeBases.git] / c_cpp / etc / calc / help / unexpected

Unexpected

    While calc is C-like, users of C will find some unexpected
    surprises in calc syntax and usage.  Persons familiar with C should
    review this file.

    Persons familiar with shell scripting may want to review this file
    as well, particularly notes dealing with command line evaluation
    and execution.


    The Comma
    =========

    The comma is also used for continuation of obj and mat creation
    expressions and for separation of expressions to be used for
    arguments or values in function calls or initialization lists.  The
    precedence order of these different uses is:  continuation,
    separator, comma operator.  For example, assuming the variables a,
    b, c, d, e, and object type xx have been defined, the arguments
    passed to f in:

            f(a, b, c, obj xx d, e)

    are a, b, c, and e, with e having the value of a newly created xx
    object.  In:

            f((a, b), c, (obj xx d), e)

    the arguments of f are b, c, d, e, with only d being a newly
    created xx object.

    In combination with other operators, the continuation use of the
    comma has the same precedence as [] and ., the separator use the
    same as the comma operator.  For example, assuming xx.mul() has
    been defined:

            f(a = b, obj xx c, d = {1,2} * obj xx e = {3,4})

    passes two arguments: a (with value b) and the product d * e of two
    initialized xx objects.


    ^ is not xor
    ** is exponentiation
    ====================

    In C, ^ is the xor operator. The expression:

            a ^ b

    yields "a to the b power", NOT "a xor b".

    Unlike in C, calc evaluates the expression:

            a ** b

    also yields "a to the b power".

    Here "a" and "b" can be a real value or a complex value:

        2^3                     3i^4
        2.5 ^ 3.5               0.5i ^ 0.25
        2.5 ^ 2.718i            3.13145i ^ 0.30103i

    In addition, "a" can be matrix.  In this case "b" must be an integer:

        mat a[2,2] = {1,2,3,4};
        a^3

    Note that 'a' == 0 and 'b' is real, then is must be >= 0 as well.
    Also 0^0 and 0**0 return the value 1.

    Be careful about the precedence of operators.  Note that:

        -1 ^ 0.5 == -1

    whereas:

        (-1) ^ 0.5 == 1i

    because the above expression in parsed as:

        -(1 ^ 0.5) == -1

    whereas:

        (-1) ^ 0.5 == 1i


    op= operators associate left to right
    =====================================

    Operator-with-assignments:

            +=  -=  *=  /=  %=  //=  &=  |=  <<=  >>=  ^=  **=

    associate from left to right instead of right to left as in C.
    For example:

            a += b *= c

    has the effect of:

            a = (a + b) * c

    where only 'a' is required to be an lvalue.  For the effect of:

            b *= c; a += b

    when both 'a' and 'b' are lvalues, use:

            a += (b *= c)


    || yields values other than 0 or 1
    ==================================

    In C:

            a || b

    will produce 0 or 1 depending on the logical evaluation
    of the expression.  In calc, this expression will produce
    either 'a' or 'b' and is equivalent to the expression:

            a ? a : b

    In other words, if 'a' is true, then 'a' is returned, otherwise
    'b' is returned.


    && yields values other than 0 or 1
    ==================================

    In C:

            a && b

    will produce 0 or 1 depending on the logical evaluation
    of the expression.  In calc, this expression will produce
    either 'a' or 'b' and is equivalent to the expression:

            a ? b : a

    In other words, if 'a' is true, then 'b' is returned, otherwise
    'a' is returned.


    / is fractional divide, // is integral divide
    =============================================

    In C:

            x/y

    performs integer division when 'x' and 'y' are integer types.
    In calc, this expression yields a rational number.

    Calc uses:

            x//y

    to perform division with integer truncation and is the equivalent to:

            int(x/y)


    | and & have higher precedence than ==, +, -, *, / and %
    ========================================================

    Is C:

            a == b | c * d

    is interpreted as:

            (a == b) | (c * d)

    and calc it is interpreted as:

            a == ((b | c) * d)


    calc always evaluates terms from left to right
    ==============================================

    Calc has a definite order for evaluation of terms (addends in a
    sum, factors in a product, arguments for a function or a matrix,
    etc.).  This order is always from left to right. but skipping of
    terms may occur for ||, && and ? : .

    Consider, for example:

            A * B + C * D

    In calc above expression is evaluated in the following order:

            A
            B
            A * B
            C
            D
            C * D
            A * B + C * D

    This order of evaluation is significant if evaluation of a
    term changes a variable on which a later term depends.  For example:

            x++ * x++ + x++ * x++

    in calc returns the value:

            x * (x + 1) + (x + 2) * (x + 3)

    and increments x as if by x += 4.  Similarly, for functions f, g,
    the expression:

            f(x++, x++) + g(x++)

    evaluates to:

            f(x, x + 1) + g(x + 2)

    and increments x three times.

    In an other example, this expression:

        1<<8/2

    evalues to 128, not 16, because <<8 is performed before the /2.


    &A[0] and A are different things in calc
    ========================================

    In calc, value of &A[0] is the address of the first element, whereas
    A is the entire array.


    *X may be used to to return the value of X
    ==========================================

    If the current value of a variable X is an octet, number or string,
    *X may be used to to return the value of X; in effect X is an
    address and *X is the value at X.


    freeing a variable has the effect of assigning the null value to it
    ===================================================================

    The freeglobals(), freestatics(), freeredc() and free() free
    builtins to not "undefine" the variables, but have the effect of
    assigning the null value to them, and so frees the memory used for
    elements of a list, matrix or object.

    Along the same lines:

            undefine *

    undefines all current user-defined functions.  After executing
    all the above freeing functions (and if necessary free(.) to free
    the current "old value"), the only remaining numbers as displayed by

            show numbers

    should be those associated with epsilon(), and if it has been
    called, qpi().


    #! is also a comment
    ====================

    In addition to the C style /* comment lines */, lines that begin with
    #! are treated as comments.

    A single # is an calc operator, not a comment.  However two or more
    ##'s in a row is a comment.  See "help pound" for more information.

        #!/usr/local/src/cmd/calc/calc -q -f

        /* a correct comment */
        ## another correct comment
        ### two or more together is also a comment
        /*
         * another correct comment
         */
        print "2+2 =", 2+2;     ## yet another comment

    This next example is WRONG:

        #!/usr/local/src/cmd/calc/calc -q -f

        # This is not a calc calc comment because it has only a single #
        # You must to start comments with ## or /*
        print "This example has invalid comments"

    See "help cscript" and "help usage" for more information.


    The { must be on the same line as an if, for, while or do
    =========================================================

    When statement is of the form { ... }, the leading { MUST BE ON
    THE SAME LINE as the if, for, while or do keyword.

    This works as expected:

        if (expr) {
            ...
        }

    However this WILL NOT WORK AS EXPECTED:

        if (expr)
        {
            ...
        }

    because calc will parse the if being terminated by
    an empty statement followed by a

        if (expr) ;
        {
            ...
        }

    In the same way, use these forms:

        for (optionalexpr ; optionalexpr ; optionalexpr) {
                ...
        }

        while (expr) {
                ...
        }

        do {
                ...
        while (expr);

    where the initial { is on the SAME LINE as the if, while,
    for or do keyword.

    NOTE: See "help statement", "help todo", and "help bugs".


    Shell evaluation of command line arguments
    ==========================================

    In most interactive shells:

        calc 2 * 3

    will frequently produce a "Missing operator" error because the '*' is
    evaluated as a "shell glob".  To avoid this you must quote or escape
    argument with characters that your interactive shell interprets.

    For example, bash / ksh / sh shell users should use:

        calc '2 * 3'

    or:

        calc 2 \* 3

    or some other form of shell meta-character escaping.


    Calc reads standard input after processing command line args
    ============================================================

    The shell command:

        seq 5 | while read i; do calc "($i+3)^2"; done

        FYI: The command "seq 5" will write 1 through 5 on separate
             lines on standard output, while read i sets $i to
             the value of each line that is read from stdin.

    will produce:

        16
        2
        3
        4
        5

    The reason why the last 4 lines of output are 2 through 5 is
    that after calc evaluates the first line and prints (1+3)^2
    (i.e., 16), calc continues to read stdin and slurps up all
    of the remaining data on the pipe.

    To avoid this problem, use:

        seq 5 | while read i; do calc "($i+3)^2" </dev/null; done

    which produces the expected results:

        16
        25
        36
        49
        64


## Copyright (C) 1999-2007  Landon Curt Noll
##
## Calc is open software; you can redistribute it and/or modify it under
## the terms of the version 2.1 of the GNU Lesser General Public License
## as published by the Free Software Foundation.
##
## Calc is distributed in the hope that it will be useful, but WITHOUT
## ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
## or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General
## Public License for more details.
##
## A copy of version 2.1 of the GNU Lesser General Public License is
## distributed with calc under the filename COPYING-LGPL.  You should have
## received a copy with calc; if not, write to Free Software Foundation, Inc.
## 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
##
## @(#) $Revision: 30.4 $
## @(#) $Id: unexpected,v 30.4 2008/05/10 13:18:09 chongo Exp $
## @(#) $Source: /usr/local/src/cmd/calc/help/RCS/unexpected,v $
##
## Under source code control:   1997/03/21 13:15:18
## File existed as early as:    1997
##
## chongo <was here> /\oo/\     http://www.isthe.com/chongo/
## Share and enjoy!  :-)        http://www.isthe.com/chongo/tech/comp/calc/