4. Statements

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 "\<nl>", where <nl> 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 "<variable> <assignment> ...", it is considered to be an assignment statement. 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. 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 section Environment Variables). 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 precision, 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 causes the side effect of assigning the printed value to 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 double quote character and contain all characters until the next double quote character. All characters are taken 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 separated by commas. Each string or expression is printed in the order of the list. No terminating newline is printed. Expressions are evaluated and their value is printed and assigned to the variable last. Strings in the print statement are printed to the output and may contain special characters. Special characters start with the backslash character (\e). 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 "\e" (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 statement1 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 expression is non-zero. It evaluates the expression before each execution 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 evaluated before each execution of the statement. If it is non-zero, the statement is evaluated. If it is zero, the loop is terminated. After each execution of the statement, expression3 is evaluated before the reevaluation of expression2. 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. (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 section Functions.)

return ( expression )

Return the value of the expression from a function. (See section Functions.) As an extension, the parenthesis are not required.

4.1 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.

Hosting by: Hurra Communications Ltd.
Generated: 2007-01-26 17:58:44