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DC(1)			    General Commands Manual			 DC(1)

NAME
       dc - an arbitrary precision calculator

SYNOPSIS
       dc

DESCRIPTION
       Dc  is a	reverse-polish desk calculator which supports unlimited	preci-
       sion arithmetic.	 It also allows	you to define and call	macros.	  Nor-
       mally  dc  reads	 from the standard input; if any command arguments are
       given to	it, they are filenames,	and dc reads and executes the contents
       of  the files before reading from standard input.  All normal output is
       to standard output; all error output is to standard error.

       A reverse-polish	calculator stores numbers on a stack.  Entering	a num-
       ber  pushes  it	on the stack.  Arithmetic operations pop arguments off
       the stack and push the results.

       To enter	a number in dc,	type  the  digits  with	 an  optional  decimal
       point.	Exponential  notation  is  not supported.  To enter a negative
       number, begin the number	with ``_''.  ``-'' cannot be used for this, as
       it  is a	binary operator	for subtraction	instead.  To enter two numbers
       in succession, separate them with spaces	or newlines.   These  have  no
       meaning as commands.

Printing Commands
       p      Prints  the  value on the	top of the stack, without altering the
	      stack.  A	newline	is printed after the value.

       P      Prints the value on the top of the stack,	popping	 it  off,  and
	      does not print a newline after.

       f      Prints  the  entire  contents of the stack without altering any-
	      thing.  This is a	good command to	use if you are lost or want to
	      figure out what the effect of some command has been.

Arithmetic
       +      Pops two values off the stack, adds them,	and pushes the result.
	      The precision of the result is determined	only by	the values  of
	      the arguments, and is enough to be exact.

       -      Pops  two	values,	subtracts the first one	popped from the	second
	      one popped, and pushes the result.

       *      Pops two values, multiplies them,	and pushes  the	 result.   The
	      number  of  fraction  digits  in the result is controlled	by the
	      current precision	value (see below) and does not depend  on  the
	      values being multiplied.

       /      Pops  two	 values,  divides the second one popped	from the first
	      one popped, and pushes the result.  The number of	fraction  dig-
	      its is specified by the precision	value.

       %      Pops two values, computes	the remainder of the division that the
	      /	command	would do, and pushes that.  The	division is done  with
	      as  many	fraction  digits as the	precision value	specifies, and
	      the remainder is also computed with that many fraction digits.

       ~      Pops two values, divides the second one popped  from  the	 first
	      one  popped.  The	quotient is pushed first, and the remainder is
	      pushed next.  The	number of fraction digits used in the division
	      is  specified  by	the precision value.  (The sequence SdSn lnld/
	      LnLd% could also accomplish this function, with slightly differ-
	      ent error	checking.)

       ^      Pops  two	values and exponentiates, using	the first value	popped
	      as the exponent and the second popped as the base.  The fraction
	      part  of the exponent is ignored.	 The precision value specifies
	      the number of fraction digits in the result.

       |      Pops three values	and computes a	modular	 exponentiation.   The
	      first  value popped is used as the reduction modulus; this value
	      must be a	non-zero number, and should be an integer.  The	second
	      popped  is  used as the exponent;	this value must	be a non-nega-
	      tive number, and any fractional part of this  exponent  will  be
	      ignored.	The third value	popped is the base which gets exponen-
	      tiated.  The precision value specifies the  number  of  fraction
	      digits  in  the  result.	For small numbers this is like the se-
	      quence Sm	lble^ Lm%, but,	unlike ^, this command will work  with
	      arbitrarily large	exponents.

       v      Pops  one	value, computes	its square root, and pushes that.  The
	      precision	value specifies	the number of fraction digits  in  the
	      result.

       Most  arithmetic	 operations  are  affected by the ``precision value'',
       which you can set with the k command.  The default precision  value  is
       zero,  which means that all arithmetic except for addition and subtrac-
       tion produces integer results.

       The remainder operation % requires some explanation: applied  to	 argu-
       ments  ``a''  and  ``b''	it produces ``a	- (b * (a / b))'', where ``a /
       b'' is computed in the current precision.

Stack Control
       c      Clears the stack,	rendering it empty.

       d      Duplicates the value on the top of the  stack,  pushing  another
	      copy of it.  Thus, ``4d*p'' computes 4 squared and prints	it.

       r      Reverses the order of (swaps) the	top two	values on the stack.

Registers
       Dc  provides  256  memory  registers, each named	by a single character.
       You can store a number or a string in a register	and retrieve it	later.

       sr     Pop the value off	the top	of the stack and store it into	regis-
	      ter r.

       lr     Copy  the	 value in register r and push it onto the stack.  This
	      does not alter the contents of r.

       Each register also contains its own stack.  The current register	 value
       is the top of the register's stack.

       Sr     Pop  the	value off the top of the (main)	stack and push it onto
	      the stack	of register r.	The previous value of the register be-
	      comes inaccessible.

       Lr     Pop the value off	the top	of register r's	stack and push it onto
	      the main stack.  The previous value in register  r's  stack,  if
	      any, is now accessible via the lr	command.

Parameters
       Dc  has three parameters	that control its operation: the	precision, the
       input radix, and	the output radix.  The precision specifies the	number
       of fraction digits to keep in the result	of most	arithmetic operations.
       The input radix controls	the interpretation of numbers  typed  in;  all
       numbers typed in	use this radix.	 The output radix is used for printing
       numbers.

       The input and output radices are	separate parameters; you can make them
       unequal,	which can be useful or confusing.  The input radix must	be be-
       tween 2 and 36 inclusive.  The output radix must	be at  least  2.   The
       precision must be zero or greater.  The precision is always measured in
       decimal digits, regardless of the current input or output radix.

       i      Pops the value off the top of the	stack and uses it to  set  the
	      input radix.

       o      Pops  the	 value off the top of the stack	and uses it to set the
	      output radix.

       k      Pops the value off the top of the	stack and uses it to  set  the
	      precision.

       I      Pushes the current input radix on	the stack.

       O      Pushes the current output	radix on the stack.

       K      Pushes the current precision on the stack.

Strings
       Dc  can	operate	on strings as well as on numbers.  The only things you
       can do with strings are print them and execute them  as	macros	(which
       means  that  the	 contents of the string	are processed as dc commands).
       All registers and the stack can	hold  strings,	and  dc	 always	 knows
       whether	any  given object is a string or a number.  Some commands such
       as arithmetic operations	demand numbers as arguments and	 print	errors
       if  given  strings.   Other  commands  can  accept either a number or a
       string; for example, the	p command can accept either and	prints the ob-
       ject according to its type.

       [characters]
	      Makes a string containing	characters (contained between balanced
	      [	and ] characters), and pushes it on the	stack.	 For  example,
	      [foo]P prints the	characters foo (with no	newline).

       a      The  top-of-stack	 is popped.  If	it was a number, then the low-
	      order byte of this number	is converted into a string and	pushed
	      onto  the	 stack.	  Otherwise the	top-of-stack was a string, and
	      the first	character of that string is pushed back.

       x      Pops a value off the stack and executes it as a macro.  Normally
	      it  should  be  a	string;	if it is a number, it is simply	pushed
	      back onto	the stack.  For	example, [1p]x executes	the  macro  1p
	      which pushes 1 on	the stack and prints 1 on a separate line.

       Macros  are  most  often	 stored	in registers; [1p]sa stores a macro to
       print 1 into register a,	and lax	invokes	this macro.

       >r     Pops two values off the stack and	compares  them	assuming  they
	      are  numbers, executing the contents of register r as a macro if
	      the original top-of-stack	is greater.  Thus, 1 2>a  will	invoke
	      register a's contents and	2 1>a will not.

       <r     Similar  but  invokes  the macro if the original top-of-stack is
	      less.

       =r     Similar but invokes the macro if	the  two  numbers  popped  are
	      equal.

       ?      Reads  a	line  from the terminal	and executes it.  This command
	      allows a macro to	request	input from the user.

       q      exits from a macro and also from the macro which invoked it.  If
	      called  from the top level, or from a macro which	was called di-
	      rectly from the top level, the q command will cause dc to	exit.

       Q      Pops a value off the stack and uses it as	a count	of  levels  of
	      macro execution to be exited.  Thus, 3Q exits three levels.  The
	      Q	command	will never cause dc to exit.

Status Inquiry
       Z      Pops a value off the stack, calculates the number	of  digits  it
	      has (or number of	characters, if it is a string) and pushes that
	      number.

       X      Pops a value off the stack, calculates the  number  of  fraction
	      digits  it has, and pushes that number.  For a string, the value
	      pushed is	0.

       z      Pushes the current stack depth; the number  of  objects  on  the
	      stack before the execution of the	z command.

Miscellaneous
       !      Will run the rest	of the line as a system	command.

       #      Will interpret the rest of the line as a comment.

       :r     Will  pop	 the top two values off	of the stack.  The old second-
	      to-top value will	be stored in the array r, indexed by  the  old
	      top-of-stack value.

       ;r     Pops  the	top-of-stack and uses it as an index into the array r.
	      The selected value is then pushed	onto the stack.

NOTES
       The array operations : and ; are	usually	only used by  traditional  im-
       plementations  of  bc.  (The GNU	bc is self contained and does not need
       dc to run.)

BUGS
       Email bug reports to bug-gnu-utils@prep.ai.mit.edu.  Be sure to include
       the word	``dc'' somewhere in the	``Subject:'' field.

GNU Project			  1997-03-25				 DC(1)

NAME | SYNOPSIS | DESCRIPTION | Printing Commands | Arithmetic | Stack Control | Registers | Parameters | Strings | Status Inquiry | Miscellaneous | NOTES | BUGS

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