94
The VIC 20
User
Guide
expressions, since this unnecessarily complicates the program.
If
you must
calculate one
of
these values, it
is
simpler and faster to do so in a separate
statement.
If
the step size
is
1 (which
is
frequently the case), you do not have to
include a step size definition. In the absence of any definition, VIC BASIC
assumes a step
size
of
1.
Therefore, the statement on line
20
could be
rewritten as follows:
10
DIM
A(99)
15
REM
USE
A
STEP
SIZE
OF
1
20
FOR
1-0
TO
99
30 A(I)-I
35
PRINT
A(l);
40
NEXT
I
S0
OOTO
S0
Also, you do not need to specify the index variable in the NEXT
statement. But if you do, it
will
make your program easier to read.
NESTED
LOOPS
The FOR-NEXT structure
is
referred to as a program loop, since
statement execution loops from FOR to NEXT and back to FOR. This loop
structure
is
very common; almost every BASIC program that you write will
include one or more such loops. Loops are
so
common that they are
frequently nested. The statement sequence occurring between
FOR
and
NEXT can be
of
any length; it can run to tens
or
even hundreds
of
state-
ments. And within these tens
or
hundreds
of
statements, additional loops
may occur. The following illustration shows a single level of nesting:
10
DIM
A(99)
20
FO~
1-0
TO
99
30 A(l)-I
40
REM
DISPLAY
ALL
VALUES
OF
A(I)
ASSIGNED
THUS
FAR
50
FOR
J
a
0
TO
I
60
PRINT
A(J)
70
NEXT
J
S0
NEXT
I
90
GOTO
99
Complex loop structures appear frequently, even in relatively short
programs. Hereis
an
example showing the
FOR
and NEXT statements,
but
none
of
the intermediate statements.
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