operators

    The operators are similar to C, but there are some differences in
    the associativity and precedence rules for some operators.	In
    addition, there are several operators not in C, and some C
    operators are missing.  A more detailed discussion of situations
    that may be unexpected for the C programmer may be found in
    the 'unexpected' help file.

    Below is a list giving the operators arranged in order of
    precedence, from the least tightly binding to the most tightly
    binding.  Except where otherwise indicated, operators at the same
    level of precedence associate from left to right.

    Unlike C, calc has a definite order for evaluation of terms (adds
    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 ? : .  For example,
    an expression of the form:

	    A * B + C * D

    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++

    returns the value of:

	    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 A || B, B is read only if A tests as false;  in A && B, B is
    read only if A tests as true.  Thus if x is nonzero,
    x++ || x++ returns x and increments x once; if x is zero,
    it returns x + 1 and increments x twice.


    ,	Comma operator.
	    a, b returns the value of b.
	    For situations in which a comma is used for another purpose
	    (function arguments, array indexing, and the print statement),
	    parenthesis must be used around the comma operator expression.
	    E.g., if A is a matrix, A[(a, b), c] evaluates a, b, and c, and
	    returns the value of A[b, c].

    +=	-=  *=	/=  %=	//=  &=	 |=  <<=  >>=  ^=  **=
	 Operator-with-assignments.
	    These associate from left to right, e.g. 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).

    =	Assignment.
	    As in C, this, when repeated, this associates from right to left,
	    e.g. a = b = c has the effect of a = (b = c).  Here both a and b
	    are to be lvalues.

    ? : Conditional value.
	    a ? b : c  returns b if a tests as true (i.e. nonzero if
	    a is a number), c otherwise.  Thus it is equivalent to:
	    if (a) return b; else return c;.
	    All that is required of the arguments in this function
	    is that the "is-it-true?" test is meaningful for a.
	    As in C, this operator associates from right to left,
	    i.e. a ? b : c ? d : e is evaluated as a ? b : (c ? d : e).

    ||	Logical OR.
	    Unlike C, the result for a || b is one of the operands
	    a, b rather than one of the numbers 0 and 1.
	    a || b is equivalent to a ? a : b, i.e. if a tests as
	    true, a is returned, otherwise b.  The effect in a
	    test like "if (a || b) ... " is the same as in C.

    &&	Logical AND.
	    Unlike C, the result for a && b is one of the operands
	    a, b rather than one of the numbers 0 and 1.
	    a && b is equivalent to a ? b : a, i.e. if a tests as
	    true, b is returned, otherwise a.  The effect in a
	    test like "if (a && b) ... " is the same as in C.

    ==	!=  <=	>=  <  >
	    Relations.

    +  -
	    Binary plus and minus and unary plus and minus when applied to
	    a first or only term.

    *  /  //  %
	    Multiply, divide, and modulo.
	    Please Note: The '/' operator is a fractional divide,
	    whereas the '//' is an integral divide.  Thus think of '/'
	    as division of real numbers, and think of '//' as division
	    of integers (e.g., 8 / 3 is 8/3 whereas 8 // 3 is 2).
	    The '%' is integral or fractional modulus (e.g., 11%4 is 3,
	    and 10%pi() is ~.575222).

    |	Bitwise OR.
	    In a | b, both a and b are to be real integers;
	    the signs of a and b are ignored, i.e.
	    a | b = abs(a) | abs(b) and the result will
	    be a non-negative integer.

    &	Bitwise AND.
	    In a & b, both a and b are to be real integers;
	    the signs of a and b are ignored as for a | b.

    ^  **  <<  >>
	    Powers and shifts.
	    The '^' and '**' are both exponentiation, e.g. 2^3
	    returns 8, 2^-3 returns .125.  Note that in a^b, if
	    'a' == 0 and 'b' is real, then is must be >= 0 as well.
	    Also 0^0 and 0**0 return the value 1.

	    For the shift operators both arguments are to be
	    integers, or if the first is complex, it is to have
	    integral real and imaginary parts.	Changing the
	    sign of the second argument reverses the shift, e.g.
	    a >> -b = a << b.  The result has the same sign as
	    the first argument except that a nonzero value is
	    reduced to zero by a sufficiently long shift to the
	    right.  These operators associate right to left,
	    e.g.  a << b ^ c = a << (b ^ c).

    +  -  !
	    Plus (+) and minus (-) have their usual meanings as unary
	    prefix operators at this level of precedence when applied to
	    other than a first or only term.

	    As a prefix operator, '!' is the logical NOT: !a returns 0 if
	    a tests as nonzero, and 1 if a tests as zero, i.e. it is
	    equivalent to a ? 0 : 1.  Be careful about
	    using this as the first character of a top level command,
	    since it is also used for executing shell commands.

	    As a postfix operator ! gives the factorial function, i.e.
	    a! = fact(a).

    ++	--
	    Pre or post incrementing or decrementing.
	    These are applicable only to variables.

    [ ]	 [[ ]]	.  ( )
	    Indexing, double-bracket indexing, element references,
	    and function calls.	 Indexing can only be applied to matrices,
	    element references can only be applied to objects, but
	    double-bracket indexing can be applied to matrices, objects,
	    or lists.

    variables  constants  .  ( )
	    These are variable names and constants, the special '.' symbol,
	    or a parenthesized expression.  Variable names begin with a
	    letter, but then can contain letters, digits, or underscores.
	    Constants are numbers in various formats, or strings inside
	    either single or double quote marks.


    The most significant difference from the order of precedence in
    C is that | and & have higher precedence than ==, +, -, *, / and %.
    For example, in C a == b | c * d is interpreted as:

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

    and calc it is:

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


    Most of the operators will accept any real or complex numbers
    as arguments.  The exceptions are:

    /  //  %
	    Second argument must be nonzero.

    ^
	    The exponent must be an integer.  When raising zero
	    to a power, the exponent must be non-negative.

    |  &
	    Both both arguments must be integers.

    <<	>>
	    The shift amount must be an integer.  The value being
	    shifted must be an integer or a complex number with
	    integral real and imaginary parts.


    See the 'unexpected' help file for a list of unexpected
    surprises in calc syntax/usage.  Persons familiar with C should
    read the 'unexpected' help file to avoid confusion.

## Copyright (C) 1999,2021  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.
##
## Under source code control:	1991/07/21 04:37:23
## File existed as early as:	1991
##
## chongo <was here> /\oo/\	http://www.isthe.com/chongo/
## Share and enjoy!  :-)	http://www.isthe.com/chongo/tech/comp/calc/
