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bc, for basic calculator (often referred to as ''bench calculator''), is "''an arbitrary precision calculator language''" with syntax similar to the C programming language. bc is typically used as either a mathematical scripting language or as an interactive mathematical shell. A typical interactive usage is typing the command bc on a Unix command prompt and entering a mathematical expression, such as ''(1 + 3) * 2'', whereupon ''8'' will be output. While bc can work with arbitrary precision, it actually defaults to zero digits after the decimal point - so the expression ''2/3'' yields ''0''. This can surprise new bc users unaware of this fact. The "-l" option to bc sets the default ''scale'' (digits after the decimal point) to 20, and adds several additional mathematical functions to the language. bc first appeared in Version 6 Unix in 1975, and was written by Robert Morris and Lorinda Cherry of Bell Labs. bc was preceded by dc, an earlier arbitrary precision calculator written by the same authors. dc could do arbitrary-precision calculations, but its Reverse Polish Notation (RPN) syntax was inconvenient for users, and therefore bc was written as a front-end to dc. bc was a very simple compiler (a single yacc source file with a few hundred lines) which converted the new, C-like, bc syntax into dc's postfix notation, and piped the results through dc. In 1991, POSIX rigorously defined and standardized bc. Two implementations of this standard survive today: The first is the traditional Unix implementation, a front-end to dc, which survives in Unix and Plan 9 systems. The second is the free software GNU bc, first released in 1991 by Philip A. Nelson. The GNU implementation has numerous extensions beyond the POSIX standard, and is no longer a front-end to dc (it is a bytecode interpreter). == POSIX bc == The POSIX standardized bc language is traditionally written as a program in the dc programming language to provide a higher level of access to the features of the dc language without the complexities of dc's terse syntax. In this form, the bc language contains single letter variable, array and function names and most standard arithmetic operators as well as the familiar control flow constructs, ( if(cond)..., while(cond)... and for(init;cond;inc)...) from C. Unlike C, an if clause may not be followed by an else.Functions are defined using a define keyword and values are returned from them using a return followed by the return value in parentheses. The auto keyword (optional in C) is used to declare a variable as local to a function.All numbers and variable contents are arbitrary precision numbers whose precision (in decimal places) is determined by the global scale variable.The numeric base of input (in interactive mode), output and program constants may be specified by setting the reserved ibase (input base) and obase (output base) variables.Output is generated by deliberately not assigning the result of a calculation to a variable. Comments may be added to bc code by use of the C / and 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Bc (programming language)」の詳細全文を読む スポンサード リンク
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