bc supports arbitrary precision numbers

$> bc<<<2+4*17 $> 70 $> echo "4+2*17" | bc $> 38 $> bc myfile.bc ... $> bc myfile.dat myfile.bc ...

a standard math library is available by command line option

bc -lif requested, the math library is defined before processing any files

bc starts by processing code from all the files listed on the command line in the order listed

after all files have been processed, bc reads from the standard input

all code is executed as it is read

if a file contains a command to halt the processor, bc will never read from the standard input

-i, --interactive

force interactive mode

-l, --mathlib

define the standard math library

-w, --warn

give warnings for extensions to POSIX bc

-s, --standard

process exactly the POSIX bc language

-q, --quiet

do not print the normal GNU bc welcome

there are two attributes of numbers, the

the

the

names begin with a letter followed by any number of letters, digits and underscores. __all letters must be lower case__

all array variable names will be followed by brackets [ ]

there are four special variables: **scale**, **ibase**, **obase**, and **last**

**scale**

digits after the decimal point. 0 by default

**ibase** and **obase**

conversion base for input and output numbers. default is base 10

the legal values of ibase are 2 through 16

**last**

a variable that has the value of the last printed number

POSIX bc does not have a last variable

these comments include any newlines (EOL)

to support the use of scripts for bc, a single line comment has been added as an extension

a single line comment starts at a # character

input numbers may contain the characters 0-9 and A-F. (__note: they must be capitals__)

a simple variable is just a name and an array variable is specified as name[index]

- expr

the negation of the expression

++ var

-- var

var ++

var --

expr + expr

expr - expr

expr * expr

expr / expr

expr % expr

to compute a%b, first a/b is computed to scale digits. that result is used to compute a-(a/b)*b to the scale of the maximum of scale+scale(b) and scale(a). if scale is set to zero and both expressions are integers this expression is the integer remainder function

expr ^ expr

the second expression __must be an integer__. (if the second expression is not an integer, a warning is generated and the expression is truncated to get an integer value). the scale of the result is scale if the exponent is negative. If the exponent is positive scale(a^b) = min(scale(a)*b, max(scale, scale(a))

relational expressions are always evaluate to 0 or 1, 0 if the relation is false and 1 if the relation is true. POSIX bc requires that relational expressions are used only in **if**, **while**, and **for** statements and that only one relational test may be done in them

expr1 < expr2

expr1 <= expr2

expr1 > expr2

expr1 >= expr2

expr1 == expr2

expr1 != expr2

boolean operations are also legal. (POSIX bc does NOT have boolean operations). the result of all boolean operations are 0 and 1

!expr

expr && expr

expr || expr

|| | left associative |

&& | left associative |

! | nonassociative |

relational operators | left associative |

assignment operator | right associative |

+ - | left associative |

* / % | left associative |

^ | right associative |

- (unary) | nonassociative |

++ -- | nonassociative |

there are a few more special expressions that are provided in bc. these have to do with user defined functions and standard functions:

**length** ( expression )

the number of significant digits in the expression

**read** ( )

the read function (an extension) will read a number from the standard input, regardless of where the function occurs. beware, this can cause problems with the mixing of data and program in the standard input. the value of the read function is __the number read from the standard input__ using the current value of the variable ibase for the conversion base

**scale** ( expression )

**sqrt** ( expression )

if the expression is negative, a run time error is generated

in fact, both a semicolon and a newline are used as statement separators. an improperly placed newline will cause a syntax error

a statement list is a series of statements separated by semicolons and newlines

expression

this statement does one of two things

if the expression starts with "

if the expression is not an assignment statement, the expression is evaluated and printed to the output. after the number is printed, a newline is printed

due to the interactive nature of bc, printing a number causes the side effect of assigning the printed value to the special variable **last**. assigning to **last** is legal and will overwrite the last printed value with the assigned value

string

the string is printed to the output. strings start with a double quote character and contain all characters until the next double quote character. no newline character is printed after the string

print

the "list" is a list of strings and expressions separated by commas. no terminating newline is printed. strings in the print statement are printed to the output and may contain special characters. special characters start with the backslash character (\). the special characters recognized by bc are "a" (alert or bell), "b" (backspace), "f" (form feed), "n" (newline), "r" (carriage return), "q" (double quote), "t" (tab), and "\" (backslash)

{ statement_list }

this is the compound statement. it allows multiple statements to be grouped together for execution

if (expression) statement1 [else statement2]

the else clause is an extension

while (expression) statement

termination of the loop is caused by a zero expression value or the execution of a **break** statement

for ([expression1]; [expression2]; [expression3]) statement

if expression1 or expression3 are missing, nothing is evaluated at the point they would be evaluated. if expression2 is missing, it is the same as substituting the value 1 for expression2. (POSIX bc requires all three expressions)

break

this statement causes a forced exit of the most recent enclosing **while** statement or **for** statement

continue

the continue statement (an extension) causes the most recent enclosing **for** statement to start the next iteration

halt

the halt statement (an extension) is an executed statement that causes the bc processor to quit only when it is executed

return

return the value 0 from a function

return ( expression )

return the value of the expression from a function. as an extension, the parenthesis are not required

quit

when the quit statement is read, the bc processor is terminated, regardless of where the quit statement is found

a function is defined as follows:

define name (parameters_list) { auto_list statement_list }a function call is just an expression of the form "name(parameters)"

parameters are numbers or arrays (an extension)

in the function definition, zero or more parameters are defined by listing their names separated by commas

all parameters are **call by value**. arrays are specified in the parameter definition by the notation "name[]"

in the function call, actual parameters are full expressions for number parameters. the same notation is used for passing arrays as for defining array parameters. the named array is passed by value to the function. parameter numbers and types are checked __when a function is called__. any mismatch in number or types of parameters will cause a runtime error

the **auto_list** is an optional list of variables that are for "local" use. these variables have their values pushed onto a stack at the start of the function. the variables are then initialized to zero and used throughout the execution of the function. at function exit, these variables are popped so that the original value (at the time of the function call) of these variables are restored

auto variables are different than traditional local variables because if function A calls function B, B may access function A's auto variables by just using the same name, unless function B has called them auto variables. Due to the fact that auto variables and parameters are pushed onto a stack, bc supports recursive functions

there are two versions of the **return** statement. the first form, "return", returns the value 0 to the calling expression. the second form, "return ( expression )", computes the value of the expression and returns that value to the calling expression. there is an implied "return (0)" at the end of every function

the standard requires the opening brace be on the same line as the define keyword and all other parts must be on following lines. optional will allow any number of newlines before and after the opening brace of the function. for example, the following definitions are legal:

define d (n) { return (2*n); } define d (n) { return (2*n); }functions may be defined as void. a void funtion returns no value. a void function does not produce any output when called by itself on an input line. the keyword

define py (y) { print "--->", y, "<---"; } py (1) --->1<---0

since py is not a void function, the call of py (1) prints the desired output and then prints the value of the function. since the function is not given an explicit **return** statement, it is zero, sothe zero is printed

define void px (x) { print "--->", x, "<---"; } px (1) --->1<---

now no zero is printed because the function is a void function

to declare a call by **variable array**, the declaration of the array parameter in the function definition looks like "*name[]". the call to the function remains the same as call by **value arrays**

names

traditional and POSIX bc have single letter names for functions, variables and arrays. they have been extended to be multi-character names that start with a letter and may contain letters, numbers and the underscore character

POSIX bc does not have logical operators

read

POSIX bc does not have a read function

print

POSIX bc does not have a print statement

continue

POSIX bc does not have a continue statement

return

POSIX bc requires parentheses around the return expression

array parameters

POSIX bc does not support array parameters in full. the POSIX grammar allows for arrays in function definitions, but does not provide a method to specify an array as an actual parameter

function format

POSIX bc requires the opening brace on the same line as the **define** keyword and the **auto** statement on the next line

=+, =-, =*, =/, =%, =^

POSIX bc does not require these "old style" assignment operators to be defined

s (x) | sine of x, x is in radians |

c (x) | cosine of x, x is in radians |

a (x) | arctangent of x, returns radians |

l (x) | natural logarithm of x |

e (x) | raising e to the value x |

j (n, x) | Bessel function of integer order n of x |

POSIXLY_CORRECT

this is the same as the -s option

BC_ENV_ARGS

this is another mechanism to get arguments to bc

the format is the same as the command line arguments. these arguments are processed first, so any files listed in the environment arguments are processed before any command line argument files

this allows the user to set up "standard" options and files to be processed at every invocation of bc

BC_LINE_LENGTH

this should be an integer specifying the number of characters in an output line for numbers

this includes the backslash and newline characters for long numbers. as an extension, the value of zero disables the multi-line feature. any other value of this variable that is less than 3 sets the line length to 70

/* input data: random variables x[i] probabilities p[i] size of arrays n read data from std input */ scale = 3 define expectation () { auto i # change the global variable y here. caution! y = 0 # x[] and p[] - are global variables. should be defined till this point while (i < n) { y += (p[i] * x[i]); i += 1 } return y } define sigma () { auto i # use global variable y here. shoul be valid till this monent # changes the global variable x[]. caution! while (i < n) { x[i] = (x[i] - y) ^ 2; i += 1 } return sqrt (expectation ()) } # user input : print "input size : " n = read () j = 0; while (j < n) { print "x[", j + 1, "] ? "; x[j] = read (); j += 1 } j = 0; while (j < n) { print "p[", j + 1, "] ? "; p[j] = read (); j += 1 } # program output : print "====================\nexpectation : ", expectation () , "\n" print "sigma : ", sigma (), "\n====================\n" quit