Chapter
10
I
BASIC Keywords
ONIGOSUB
Statement
ON
n
GOSUB
Zine[,Zine,
...
I
Looks
at
n
and transfers program control
to
the subroutine indi-
cated by the nth line listed.
For example, if
n
equals
1,
BASIC branches to the first line
listed; if
n
equals 2, BASIC branches to the second line listed.
Line
is the subroutine line at which execution begins when
BASIC makes the branch.
N
must be a number in the range 0
to
255. If necessary, BASIC
rounds
n
to
an integer before evaluating it. If
n
is 0 or greater
than the number
of
line numbers listed, BASIC continues with
the next statement. If
n
is negative
or
is greater than 255, an
“Illegal function call” error occurs.
Use the RETURN statement
to
exit the subroutine.
Example
10
ON
Y
GOSUB
1000,
2000,
3000
If
Y
equals
1,
BASIC branches to a subroutine, beginning
at
Line 1000. If
Y
equals 2, BASIC branches to
a
subroutine, be-
ginning at Line 2000. If
Y
equals 3, BASIC branches to a sub-
routine, beginning at Line 3000.
If
Y
is outside the range
1
to
3, BASIC either continues with the
next statement
or
generates an “Illegal function call,”
as
men-
tioned earlier.
229
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