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bc

bc [options ] [files ]

Interactively perform arbitrary-precision arithmetic or convert numbers from one base to another. Input can be taken from files or read from the standard input. To exit, type quit or EOF .

Options

-c

Do not invoke dc ; compile only. (Since bc is a preprocessor for dc , bc normally invokes dc .)

-l

Make available functions from the math library.

bc is a language (and compiler) whose syntax resembles that of C. bc consists of identifiers, keywords, and symbols, which are briefly described here. Examples follow at the end.

Identifiers

An identifier is a single character, consisting of the lowercase letters a-z. Identifiers are used as names for variables, arrays, and functions. Within the same program you may name a variable, an array, and a function using the same letter. The following identifiers would not conflict:

x

Variable x .

x[ i ]

Element i of array x . i can range from 0 to 2047 and can also be an expression.

x(y,z)

Call function x with parameters y and z .

Input/Output Keywords

ibase , obase , and scale each store a value. Typing them on a line by themselves displays their current value. More commonly, you would change their values through assignment. Letters A-F are treated as digits whose values are 10-15.

ibase = n

Numbers that are input (e.g., typed) are read as base n (default is 10).

obase = n

Numbers displayed are in base n (default is 10). Note: once ibase has been changed from 10, use digit "A" to restore ibase or obase to decimal.

scale = n

Display computations using n decimal places (default is 0, meaning that results are truncated to integers). scale is normally used only for base-10 computations.

Statement Keywords

A semicolon or a newline separates one statement from another. Curly braces are needed only when grouping multiple statements.

if ( rel-expr ) { statements }

Do one or more statements if relational expression rel-expr is true; for example:

if (x == y) i = i + 1

while ( rel-expr ) { statements }

Repeat one or more statements while rel-expr is true; for example:

while (i > 0) {p = p*n; q = a/b; i = i-1}

for ( expr1 ; rel-expr ; expr2 ) { statements }

Similar to while ; for example, to print the first 10 multiples of 5, you could type:

for (i = 1; i <= 10; i++) i*5

break

Terminate a while or for statement.

quit

Exit bc .

Function Keywords

define j ( k ) {

Begin the definition of function j having a single argument k . Additional arguments are allowed, separated by commas. Statements follow on successive lines. End with a } .

auto x , y

Set up x and y as variables local to a function definition, initialized to 0 and meaningless outside the function. Must appear first.

return( expr )

Pass the value of expression expr back to the program. Return 0 if ( expr ) is left off. Used in function definitions.

sqrt( expr )

Compute the square root of expression expr .

length( expr )

Compute how many digits are in expr .

scale( expr )

Same, but count only digits to the right of the decimal point.

Math Library Functions

These are available when bc is invoked with -l . Library functions set scale to 20.

s( angle )

Compute the sine of angle , a constant or expression in radians.

c( angle )

Compute the cosine of angle , a constant or expression in radians.

a( n )

Compute the arctangent of n , returning an angle in radians.

e( expr )

Compute e to the power of expr .

l( expr )

Compute natural log of expr .

j( n , x )

Compute Bessel function of integer order n .

Operators

These consist of operators and other symbols. Operators can be arithmetic, unary, assignment, or relational.

Arithmetic

+ - * / % ^

Unary

- ++ --

Assignment

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

Relational

< <= > >= == !=

Other Symbols

/* */

Enclose comments.

( )

Control the evaluation of expressions (change precedence). Can also be used around assignment statements to force the result to print.

{ }

Used to group statements.

[ ]

Array index.

" text "

Use as a statement to print text .

Examples

Note that when you type some quantity (a number or expression), it is evaluated and printed, but assignment statements produce no display:

ibase = 8

         Octal input

20

                Evaluate this octal number

16

                Terminal displays decimal value

obase = 2

         Display output in base 2 instead of base 10

20

                Octal input

10000             Terminal now displays binary value

ibase = A

         Restore base 10 input

scale = 3

         Truncate results to three places

8/7

               Evaluate a division

1.001001000

       Oops! Forgot to reset output base to 10

obase = 10

        Input is decimal now, so "A" isn't needed

8/7


1.142             Terminal displays result (truncated)

The following lines show the use of functions:

define p(r,n){

    Function p uses two arguments

  auto v

          v is a local variable

  v = r^n

         r raised to the n power

  return(v)}

       Value returned

scale = 5


x = p(2.5,2)

      x = 2.5 ^ 2

x

                 Print value of x

6.25
length(x)

         Number of digits

3
scale(x)

          Number of places to right of decimal point

2


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