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* Pseudo 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 ( 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. ( Functions.)
`RETURN' ( EXPRESSION )
Return the value of the expression from a function. (
Functions.) As an extension, the parenthesis are not required.
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