Dc (computer program)
dc is a cross-platform reverse-polish desk calculator which supports arbitrary-precision arithmetic. It is one of the oldest Unix utilities, predating even the invention of the C programming language. Like other utilities of that vintage, it has a powerful set of features but an extremely terse syntax. Traditionally, the bc calculator program (with infix notation) was implemented on top of dc.
This article provides some examples in an attempt to give a general flavour of the language; for a complete list of commands and syntax, one should consult the man page for one's specific implementation.
dc is the oldest surviving Unix language. When its home Bell Labs received a PDP-11, dc—written in B—was the first language to run on the new computer, even before an assembler.
To multiply four and five in dc (note that most of the whitespace is optional):
You can also get the result with the commands:
or
This translates into "push four and five onto the stack, then, with the multiplication operator, pop two elements from the stack, multiply them and push the result back on the stack." Then the 'p' command is used to examine (print out to the screen) the top element on the stack. The 'q' command quits the invoked instance of dc. Note that numbers must be spaced from each other even as some operators need not be.
The arithmetic precision is changed with the command 'k', which sets the number of fractional digits (the number of digits following the point) to be used for arithmetic operations. Since the default precision is zero, this sequence of commands produces '0' as a result:
By adjusting the precision with 'k', arbitrary number of decimal places can be produced. This command sequence outputs '.66666'.
To evaluate : ('v' computes the square root of the top of the stack and '_' is used to input a negative number):
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