Atari 400 Users Handbooks page 69

Introduction to Atar i BASIC 67
The loop will continue to be executed until
r\
atta ins a value
greater than 20. When this occu rs , the statement following the
NEXT statement will be executed.
In our preceding example, A is known as an index variable. If the
optional keyword STEP is not in cluded w ith the FOR statement,
the index variable will be incremented by 1
every
time the NEXT
statement is executed.
STEP can be included at the end of a FOR statement to change
the value by which th e inde x variable is incremented . The
integer appearing after STEP is the new in creme nt. For example,
if our preceding exa mple were changed as follows ,
100 FOR A
=
1 TO 20 STEP 2
200 X
=
A
A
2
300 PRINT X
400 NEXT A
500 END
the inde x variable A would be incremented by 2 eve ry time the
NEXT state ment was executed.
Nested Loops
One loop can be placed inside of another loop. Th e innermost
loop is known as a nested loop. The following program contains
a nested loop.
100
P
=
1000
200 FOR Y
=
1 TO 10
300 FOR
Q
=
1 TO 4
400 P
=
P + P
*
.02
500 NEXT
Q
600 NEXT Y
650 PRINT P
700 END
Our preceding examp le is used to calculate the value of 1000
after 10 years with an interest rate of 8% compounded quarterly.
On e error that yo u should take care to
avoid
when using nested