bc starts executing code from files on the command line then reads from the standard input.
There are some similarities in the syntax to C .

--warn -w	Give warnings for extensions to POSIX bc.
--standard -s	Process exactly the POSIX bc language.
--quiet -q	Do not print the welcome. bc 1.06 Copyright 1991-1994, 1997, 1998, 2000 Free Software Foundation, Inc. This is free software with ABSOLUTELY NO WARRANTY. For details type `warranty'.
--version -v	Print the version number and copyright and quit.
--mathlib -l	Define the math library.

NUMBERS are arbitrary precision in both the integer part and the fractional part.
are represented internally in decimal and all computation is done in decimal.
Numbers have attributes :

1. length :number of significant digits
2. scale : number of digits after the decimal point.

VARIABLES store numbers,
named begining with a lowercase letter followed by any number of lowercase letters, digits and underscores.
POSIX names are a single lower case letter.

1. simple:
2. arrays: array variable names are followed by brackets ([ ] ).
3. There are four special variables, scale, ibase, obase, and last.
   • scale defines how some operations use digits after the decimal point. The default value of scale is 0.
   • ibase and obase define the conversion base for input and output numbers and default to base 10. The legal values of ibase are 2 through 16.
   • last is a variable that has the value of the last printed number. (extension)

• || operator, left associative
• && operator, left associative
• ! operator, nonassociative
• Relational operators, left associative
• Assignment operator, right associative
• + and - operators, left associative
• *, / and % operators, left associative
• ^ operator, right associative
• unary - operator, nonassociative
• ++ and -- operators, nonassociative

STATEMENTS (as in most algebraic languages) provide the sequencing of expression evaluation. In bc statements are executed "as soon as possible." Execution happens when a newline in encountered and there is one or more complete statements. Due to this immediate execution, newlines are very important in bc. In fact, both a semicolon and a newline are used as statement separators. An improperly placed newline will cause a syntax error. Because newlines are statement separators, it is possible to hide a newline by using the backslash character. The sequence "\", where is the newline appears to bc as whitespace instead of a newline. A statement list is a series of statements separated by semicolons and newlines. The following is a list of bc statements and what they do: (Things enclosed in brackets ([]) are optional parts of the statement.)
expression This statement does one of two things. If the expression starts with " ...", it is considered to be an assignment statement. If the expression is not an assignment statement, the expression is evaluated and printed to the out put. After the number is printed, a newline is printed. For example, "a=1" is an assignment statement and "(a=1)" is an expression that has an embedded assignment. All numbers that are printed are printed in the base specified by the variable obase. The legal values for obase are 2 through BC_BASE_MAX.
(See the section LIMITS.) For bases 2 through 16, the usual method of writing numbers is used. For bases greater than 16, bc uses a multi-character digit method of printing the numbers where each higher base digit is printed as a base 10 number.
The multi-character digits are separated by spaces. Each digit contains the number of characters required to represent the base ten value of "obase-1". Since numbers are of arbitrary preci sion, some numbers may not be printable on a single output line.
These long numbers will be split across lines using the "\" as the last character on a line. The maximum number of characters printed per line is 70. Due to the interactive nature of bc printing a number cause the side effect of assigning the printed value the the special variable last. This allows the user to recover the last value printed without having to retype the expression that printed the number. Assigning to last is legal and will overwrite the last printed value with the assigned value. The newly assigned value will remain until the next number is printed or another value is assigned to last. (Some installations may allow the use of a single period (.) which is not part of a number as a short hand notation for for last.)
string The string is printed to the output. Strings start with a dou ble quote character and contain all characters until the next double quote character. All characters are take literally, including any newline. No newline character is printed after the string.

print list The print statement (an extension) provides another method of output. The "list" is a list of strings and expressions sepa rated by commas. Each string or expression is printed in the order of the list. No terminating newline is printed. Expres sions are evaluated and their value is printed and assigned the the variable last. Strings in the print statement are printed to the output and may contain special characters. Special charac ters start with the backslash character (\). The special char acters 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).
Any other character following the backslash will be ignored.

{ statement_list } This is the compound statement. It allows multiple statements to be grouped together for execution.

if ( expression ) statement1 [else statement2] The if statement evaluates the expression and executes state ment1 or statement2 depending on the value of the expression.
If the expression is non-zero, statement1 is executed. If statement2 is present and the value of the expression is 0, then statement2 is executed. (The else clause is an extension.)
while ( expression ) statement The while statement will execute the statement while the expres sion is non-zero. It evaluates the expression before each exe cution of the statement. Termination of the loop is caused by a zero expression value or the execution of a break statement.

for ( [expression1] ; [expression2] ; [expression3] ) statement The for statement controls repeated execution of the statement.
Expression1 is evaluated before the loop. Expression2 is evalu ated before each execution of the statement. If it is non-zero, the statement is evaluated. If it is zero, the loop is termi nated. After each execution of the statement, expression3 is evaluated before the reevaluation of expression2. If expres sion1 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. (The optional expressions are an extension. POSIX bc requires all three expressions.) The following is equivalent code for the for statement: expression1; while (expression2) { statement; expression3; }
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. For example, "if (0 == 1) halt" will not cause bc to terminate because the halt is not executed.

return Return the value 0 from a function. (See the section on func tions.)
return ( expression ) Return the value of the expression from a function. (See the section on functions.) PSEUDO STATEMENTS These statements are not statements in the traditional sense. They are not executed statements. Their function is performed at "compile" time.

limits Print the local limits enforced by the local version of bc.
This is an extension.

quit When the quit statement is read, the bc processor is terminated, regardless of where the quit statement is found. For example, "if (0 == 1) quit" will cause bc to terminate.

warranty Print a longer warranty notice. This is an extension.

FUNCTIONS provide a method of defining a computation that can be executed later. Functions in bc always compute a value and return it to the caller. Function definitions are "dynamic" in the sense that a function is undefined until a definition is encountered in the input.
That definition is then used until another definition function for the same name is encountered. The new definition then replaces the older definition. A function is defined as follows: define name ( parameters ) { newline 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. Numbers are only call by value parameters. Arrays are only call by variable. 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 variable to the function. Since function definitions are dynamic, parameter numbers and types are checked when a function is called. Any mismatch in number or types of parameters will cause a runtime error. A runtime error will also occur for the call to an undefined function.

The auto_list is an optional list of variables that are for "local" use. The syntax of the auto list (if present) is "auto name, ... ;".
(The semicolon is optional.) Each name is the name of an auto variable. Arrays may be specified by using the same notation as used in parameters. 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. The parameters are really auto variables that are initialized to a value provided in the function call. Auto variables are different than traditional local variables in the fact that 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.

The function body is a list of bc statements. Again, statements are separated by semicolons or newlines. Return statements cause the termination of a function and the return of a value. 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. This allows a function to terminate and return 0 without an explicit return statement.

Functions also change the usage of the variable ibase. All constants in the function body will be converted using the value of ibase at the time of the function call. Changes of ibase will be ignored during the execution of the function except for the standard function read, which will always use the current value of ibase for conversion of numbers.

MATH LIBRARY If bc is invoked with the -l option, a math library is preloaded and the default scale is set to 20. The math functions will calculate their results to the scale set at the time of their call. The math library defines the following functions:
s (x) sine of x, x is in radians.
c (x) cosine of x, x is in radians.
a (x) arctangent of x, arctangent returns radians.
l (x) natural logarithm of x.
e (x) exponential function of raising e to the value x.
j (n,x) bessel function of integer order n of x.

EXAMPLES In /bin/sh, the following will assign the value of "pi" to the shell variable pi.

pi=$(echo "scale=10; 4*a(1)" | bc -l)
following definition of the exponential function used in the math library, written in POSIX bc.

              scale = 20
              /* Uses the fact that e^x = (e^(x/2))^2
                 When x is small enough, we use the series:
                   e^x = 1 + x + x^2/2! + x^3/3! + ...      

              */          define e(x) {
                auto  a, d, e, f, i, m, v, z
                /* Check the sign of x. */
                if (x<0) {
                  m = 1
                  x = -x
                }
                /* Precondition x. */
                z = scale;
                scale = 4 + z + .44*x;
                while (x > 1) {
                  f += 1;
                  x /= 2;
                }
          
                /* Initialize the variables. */
                v = 1+x
                a = x
                d = 1
           
                for (i=2; 1; i++) {
                  e = (a *= x) / (d *= i)
                  if (e == 0) {
                    if (f>0) while (f--)  v = v*v;
                    scale = z
                    if (m) return (1/v);
                    return (v/1);
                  }
                  v += e
                }
              }

       scale=2
              print "\nCheck book program!\n"
       is best kept in a file so that it can be used many times without having to retype it at every use.      
           
              scale=2
              print "\nCheck book program!\n"
              print "  Remember, deposits are negative transactions.\n"
              print "  Exit by a 0 transaction.\n\n"
          
              print "Initial balance? "; bal = read()
              bal /= 1
              print "\n"
              while (1) {
                "current balance = "; bal
                "transaction? "; trans = read()
                if (trans == 0) break;
                bal -= trans
                bal /= 1
              }
              quit
           

              define f (x) {
                if (x <= 1) return (1);
                return (f(x-1) * x);
              }
           

a = 1
              b = 2

{ a = 1
         b = 2 }