Commodore 128D - Page 280

HEADER (A$),IAB,D0,U9
HELP
This example HEADERS the
diskette with the name
specified by the variable A$,
and the i.d. specified by the
two characters following the
I, on drive 0, device
number 9.
—Highlight the line where the error occurred
HELP
The HELP command is used after an error has been reported in a
program. When HELP is typed in 40-column format, the line where
the error occurs is listed, with the portion containing the error dis
played in reverse field. In 80-column format, the portion of the line
where the error occurs is underlined.
IF/THEN/ELSE
—Evaluate a conditional expression and execute portions of a pro
gram depending on the outcome of the expression
IF expression THEN statements [:ELSE else-clause]
The IF... THEN statement evaluates a BASIC expression and takes
one of two possible courses of action depending upon the outcome
of the expression. If the expression is true, the statement(s) following
THEN is executed. This can be any BASIC statement. If the expres
sion is false, the program resumes with the program line immedi
ately following the program line containing the IF statement, unless
an ELSE clause is present. The entire IF... THEN statement must be
contained within 160 characters. Also see BEGIN/BEND.
The ELSE clause, if present, must be on the same line as the IF...
THEN portion of the statement, and separated from the THEN
clause by a colon. When an ELSE clause is present, it is executed
only when the expression is false. The expression being evaluated
may be a variable or formula, in which case it is considered true if
nonzero, and false if zero. In most cases, there is an expression
involving relational operators (=,<,>,< = ,> = ,<».
The IF... THEN statement can take two additional forms:
IF expression THEN line number
or:
IF expression GOTO line number
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BASIC 7.0 ENCYCLOPEDIA—Basic Commands and Statements