HP 3000 Manuals HP 3000 Manuals
FOR
The FOR and NEXT statements define a loop that is repeated until the
value of the loop control variable is greater than or less than a
specified value. The value of the loop control variable can increase or
decrease.
Syntax
FOR num_var=num_expr1 TO num_expr2 [STEP num_expr3] [stmt]...
NEXT num_var
Parameters
num_var The numeric loop control variable that assumes the
values num_expr1, num_expr1+num_expr3,
num_expr1+(2*num_expr3), etc. on successive executions
of the loop body. The loop body executes once for each
value that is less than or equal to num_expr2 (if
num_expr3 is positive) or greater than or equal to
num_expr2 (if num_expr3 is negative).
The num_var in the FOR and NEXT statements must be the
same.
num_expr1 The initial value that num_var is assigned.
num_expr2 Value that num_var is compared to before the loop body
is executed. If num_expr3 is positive and num_var >
num_expr2, the loop body is not executed. Similarly, if
num_expr3 is negative and num_var < num_expr2, the loop
body is not executed.
num_expr3 Amount that num_var is incremented by (if num_expr2 is
positive) or decremented (if num_expr2 is negative)
following execution of the statements in the loop body.
stmt If num_expr2 is positive, this statement or statements
executes each time num_var <= num_expr2. If num_var is
negative, this statement executes each time num_var >=
num_expr2. These statements constitute the loop body.
Examples
10 FOR I=2 TO 10 STEP 2 !This will loop 5 times.
20 PRINT "I=",I !Values are: 2,4,6,8,10
30 PRINT "I+I=",I+I !Values are: 4,8,12,16,20
40 PRINT "I*I=",I*I !Values are: 4,16,36,64,100
50 NEXT I
10 FOR J=4 TO 1 STEP -1 !This will loop 4 times
20 PRINT J !Values 4,3,2,1
30 NEXT J
100 FOR K=1 TO 20 !This will loop 20 times
110 PRINT K !Values 1,2,3,...,19,20
120 NEXT K
If num_expr3 is positive, and the first value is greater than the last
value, or if num_expr3 is negative, and the first value is less than the
last value, then the loop is never executed.
20 FOR I=10 TO 1
30 PRINT I !Never executed
40 NEXT I
FOR constructs can be nested.
100 FOR I=1 TO 3 !Outside FOR loop
110 FOR J=1 TO 5 !Inside FOR loop
120 PRINT "*";
130 NEXT J
135 PRINT
140 NEXT I
999 END
The above program prints:
*****
*****
*****
NOTE An error occurs if nested loops have the same loop control variable
(num_var).
If you use mixed mode arithmetic on the control variable, the
results can be unpredictable. For example, if I is an integer, and
the STEP value is .1, STEP is rounded to zero.
Entering from a statement other than the FOR statement the body of a FOR
loop causes an error at the NEXT statement, because no FOR statement is
active.