statement

来自「Calc Software Package for Number Calc」· 代码 · 共 348 行

Statements

    Statements are very much like C statements.	 Most statements act
    identically to those in C, but there are minor differences and
    some additions.  The following is a list of the statement types,
    with explanation of the non-C statements.

    Statements are generally terminated with semicolons or { ... }.

    C-like statements
    -----------------
    { statement }
    { statement; ... statement }


    C-like flow control
    -------------------
    if (expr) statement
    if (expr) statement else statement
    for (optionalexpr ; optionalexpr ; optionalexpr) statement
    while (expr) statement
    do statement while (expr)

	    These all work like in normal C.

	    IMPORTANT NOTE: 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.

	    See 'help expression' for details on expressions.
	    See 'help builtin' for details on calc builtin functions.
	    See 'help unexpanded' for things C programmers do not expect.
	    See also 'help todo' and 'help bugs'.


    C-like flow breaks
    ------------------
    continue
    break
    goto label
	    These all work like in normal C.

	    See 'help expression' for details on expressions.
	    See 'help builtin' for details on calc builtin functions.


    return
    ------
    return
    return expr
    return ( expr )
	    This returns a value from a function.  Functions always
	    have a return value, even if this statement is not used.
	    If no return statement is executed, or if no expression
	    is specified in the return statement, then the return
	    value from the function is the null type.


    switch
    ------
    switch (expr) { caseclauses }
	    Switch statements work similarly to C, except for the
	    following.	A switch can be done on any type of value,
	    and the case statements can be of any type of values.
	    The case statements can also be expressions calculated
	    at runtime.	 The calculator compares the switch value
	    with each case statement in the order specified, and
	    selects the first case which matches.  The default case
	    is the exception, and only matches once all other cases
	    have been tested.


    matrix
    ------
    mat variable [dimension] [dimension] ...
    mat variable [dimension, dimension, ...]
    mat variable [] = { value, ... }
	    This creates a matrix variable with the specified dimensions.
	    Matrices can have from 1 to 4 dimensions.  When specifying
	    multiple dimensions, you can use either the standard C syntax,
	    or else you can use commas for separating the dimensions.
	    For example, the following two statements are equivalent,
	    and so will create the same two dimensional matrix:

		    mat foo[3][6];
		    mat foo[3,6];

	    By default, each dimension is indexed starting at zero,
	    as in normal C, and contains the specified number of
	    elements.  However, this can be changed if a colon is
	    used to separate two values.  If this is done, then the
	    two values become the lower and upper bounds for indexing.
	    This is convenient, for example, to create matrices whose
	    first row and column begin at 1.  Examples of matrix
	    definitions are:

		    mat x[3]	one dimension, bounds are 0-2
		    mat foo[4][5]	two dimensions, bounds are 0-3 and 0-4
		    mat a[-7:7] one dimension, bounds are (-7)-7
		    mat s[1:9,1:9]	two dimensions, bounds are 1-9 and 1-9

	    Note that the MAT statement is not a declaration, but is
	    executed at runtime.  Within a function, the specified
	    variable must already be defined, and is just converted to
	    a matrix of the specified size, and all elements are set
	    to the value of zero.  For convenience, at the top level
	    command level, the MAT command automatically defines a
	    global variable of the specified name if necessary.

	    Since the MAT statement is executed, the bounds on the
	    matrix can be full expressions, and so matrices can be
	    dynamically allocated.  For example:

		    size = 20;
		    mat data[size*2];

	    allocates a matrix which can be indexed from 0 to 39.

	    Initial values for the elements of a matrix can be specified
	    by following the bounds information with an equals sign and
	    then a list of values enclosed in a pair of braces.	 Even if
	    the matrix has more than one dimension, the elements must be
	    specified as a linear list.	 If too few values are specified,
	    the remaining values are set to zero.  If too many values are
	    specified, a runtime error will result.  Examples of some
	    initializations are:

		    mat table1[5] = {77, 44, 22};
		    mat table2[2,2] = {1, 2, 3, 4};

	    When an initialization is done, the bounds of the matrix
	    can optionally be left out of the square brackets, and the
	    correct bounds (zero based) will be set.  This can only be
	    done for one-dimensional matrices.	An example of this is:

		    mat fred[] = {99, 98, 97};

	    The MAT statement can also be used in declarations to set
	    variables as being matrices from the beginning.  For example:

		    local mat temp[5];
		    static mat strtable[] = {"hi", "there", "folks");


    object
    ------
    obj type { elementnames } optionalvariables
    obj type variable
	    These create a new object type, or create one or more
	    variables of the specified type.  For this calculator,
	    an object is just a structure which is implicitly acted
	    on by user defined routines.  The user defined routines
	    implement common operations for the object, such as plus
	    and minus, multiply and divide, comparison and printing.
	    The calculator will automatically call these routines in
	    order to perform many operations.

	    To create an object type, the data elements used in
	    implementing the object are specified within a pair
	    of braces, separated with commas.  For example, to
	    define an object will will represent points in 3-space,
	    whose elements are the three coordinate values, the
	    following could be used:

		    obj point {x, y, z};

	    This defines an object type called point, whose elements
	    have the names x, y, and z.	 The elements are accessed
	    similarly to structure element accesses, by using a period.
	    For example, given a variable 'v' which is a point object,
	    the three coordinates of the point can be referenced by:

		    v.x
		    v.y
		    v.z

	    A particular object type can only be defined once, and
	    is global throughout all functions.	 However, different
	    object types can be used at the same time.

	    In order to create variables of an object type, they
	    can either be named after the right brace of the object
	    creation statement, or else can be defined later with
	    another obj statement.  To create two points using the
	    second (and most common) method, the following is used:

		    obj point p1, p2;

	    This statement is executed, and is not a declaration.
	    Thus within a function, the variables p1 and p2 must have
	    been previously defined, and are just changed to be the
	    new object type.  For convenience, at the top level command
	    level, object variables are automatically defined as being
	    global when necessary.

	    Initial values for an object can be specified by following
	    the variable name by an equals sign and a list of values
	    enclosed in a pair of braces.  For example:

		    obj point pt = {5, 6};

	    The OBJ statement can also be used in declarations to set
	    variables as being objects from the beginning.  If multiple
	    variables are specified, then each one is defined as the
	    specified object type.  Examples of declarations are:

		    local obj point temp1;
		    static obj point temp2 = {4, 3};
		    global obj point p1, p2, p3;


    print expressions
    -----------------
    print expr
    print expr, ... expr
    print expr: ... expr
	    For interactive expression evaluation, the values of all
	    typed-in expressions are automatically displayed to the
	    user.  However, within a function or loop, the printing of
	    results must be done explicitly.  This can be done using
	    the 'printf' or 'fprintf' functions, as in standard C, or
	    else by using the built-in 'print' statement.  The advantage
	    of the print statement is that a format string is not needed.
	    Instead, the given values are simply printed with zero or one
	    spaces between each value.

	    Print accepts a list of expressions, separated either by
	    commas or colons.  Each expression is evaluated in order
	    and printed, with no other output, except for the following
	    special cases.  The comma which separates expressions prints
	    a single space, and a newline is printed after the last
	    expression unless the statement ends with a colon.	As
	    examples:

		    print 3, 4;			prints "3 4" and newline.
		    print 5:;			prints "5" with no newline.
		    print 'a' : 'b' , 'c';	prints "ab c" and newline.
		    print;			prints a newline.

	    For numeric values, the format of the number depends on the
	    current "mode" configuration parameter.  The initial mode
	    is to print real numbers, but it can be changed to other
	    modes such as exponential, decimal fractions, or hex.

	    If a matrix or list is printed, then the elements contained
	    within the matrix or list will also be printed, up to the
	    maximum number specified by the "maxprint" configuration
	    parameter.	If an element is also a matrix or a list, then
	    their values are not recursively printed.  Objects are printed
	    using their user-defined routine.  Printing a file value
	    prints the name of the file that was opened.


    Also see the help topic:

	    help command	top level commands
	    help expression	calc expression syntax
	    help builtin	calc builtin functions
	    help usage	    	how to invoke the calc command and calc -options

    You may obtain help on individual builtin functions.  For example:

	    help asinh
	    help round

    See:
    	    help builtin

    for a list of builtin functions.

    Some calc operators have their own help pages:

	    help ->
	    help *
	    help .
	    help %
	    help //
	    help #

    See also:

	    help help


## Copyright (C) 1999-2007  Landon Curt Noll
##
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## 59 Temple Place, Suite 330, Boston, MA  02111-1307, USA.
##
## @(#) $Revision: 29.4 $
## @(#) $Id: statement,v 29.4 2007/02/07 00:29:06 chongo Exp $
## @(#) $Source: /usr/local/src/cmd/calc/help/RCS/statement,v $
##
## 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/
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