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Commands
and
Statements
6-14
ON ... GOSUB
The
ON
... GOSUB statement transfers
program
control to one
or
one
of
a set
of
subroutines.The line numbers
of
the first lines
of
these subroutines follow sequen-
tially, separated by commas.
If
the expression evaluates
to
3, control transfers to the
third line
number
following GOSUB.
ON
expression
GOSUB line
number
[,Iine number] ...
10
INPUT A
20
ON
A GOSUB 200,300
ON ...
GOTO
The ON ...
GOTO
statement transfers program control to one
or
one
of
a set
of
line
numbers.
The
expression X
is
evaluated
and
control
is
transferred to the
"nth"
line
number following the line containing the
ON
...
GOTO
instruction.
If
the expression
evaluates
to
3, control transfers
to
the third line number following GOSUB.
ON
expression
GOTO line
number
[,Iine number] ...
10
INPUT A
20
ON
A GOTO
500,510,520
OPEN
The
OPEN
statement makes
an
ISIS-II file available
to
BASIC.
It
also
associates a file number from 1
to
6 with
the
file. File type can be I,
0,
or
R.
Random
110
files are specified by
an
R, sequential input files are specified by
an I,
and
sequential
output
files are specified by
an
0,
as shown in the syn-
tactic
format
below.
The
file number
is
an
integer expression greater
than
0
and less
than
or
equal to 6,
is
preceded by a
"#"
sign, and
is
used
to
reference
the file in
110
transactions.
Only six files may be open
at
one time.
Note
that
SAVE, LOAD, DSKF; DIR
and
MERGE
all require a file, so a maximum
of
five files may be open before
they are executed.
BASIC-SO buffers files, so if :CI:
is
opened for input, BASIC-SO will wait for
the first line
of
console input.
OPEN type, [I] file number, filename
where type
is
a string expression equal to
"0",
"I"
or
"R".
In the example below,
the file SYSLIB
is
opened as a
random
I/O
file, with number 4.
OPEN
"R"
,#4,
"SYSLlB"
BASIC-SO