Creating a FOR ... TO loop that can change its TO limit?

[notwhoyouthink]

1 Z=10
2 FOR A = 1 TO Z
3 IF TEST-CONDITION=1 THEN 4 ELSE 7
4 Z=Z+1 !MODIFY THE LOOP LIMIT TO RUN A EXTRA TIME

5 DO SOMETHING

6 GOTO 8
7 DO SOMETHING DIFFERENT

8 NEXT A

What i want is a loop that changes itself to run extra times if needed, based on whether a certain conditional variable is 1 or 0.
I am fairly certain something like this can be done in languages like C, but is it possible in Basic/XB?

Edited December 22, 2017 by notwhoyouthink

[+OLD CS1]

The ending constraint is evaluated at the time the FOR statement is executed. I am pretty certain the stepping value is, as well. However, you can manipulate the counter variable.

 

For instance:

10 Z=10
20 FOR A=1 TO Z
25 PRINT A
30 A=A+2
40 NEXT A

This will print 1, 4, 7, then 10.

 

And this:

10 Z=10
20 FOR A=1 TO Z
30 PRINT A
40 IF A<>5 OR Z=0 THEN 60
50 A=A-4 :: Z=0
60 NEXT A

Will print 1,2,3,4,5,2,3,4,5,6,7,8,9,10

 

EDIT: Yes, the stepping value is evaluated at the time of FOR execution, as well:

 

 

10 Z=20
15 I=2
20 FOR A=1 TO Z STEP I
25 I=1
30 PRINT A
40 IF A<>5 OR Z=0 THEN 60
50 A=A-4 :: Z=0
60 NEXT A

Prints 1,3,5,3,5,7,9,11,13,15,17,19

[+OLD CS1]

You could manipulate a FOR/NEXT loop to be a DO/WHILE loop like this:

10 FOR A=-1 TO 0
20 REM DOING SOMETHING
30 REM DOING SOMETHING MORE
40 A=TESTCONDITION
50 NEXT A

0 (zero) is "false," and any non-zero value is "true," but the evaluation of a condition is -1 for "true." Therefore, setting the counter variable in 40 to a true/false -1/0 condition (more like a DO/UNTIL) will control the loop without the use of IF/THEN, GOTO, or ON GOTO.

[Willsy]

1 Z=10

2 FOR A = 1 TO Z

3 IF TEST-CONDITION=1 THEN 4 ELSE 7

4 Z=Z+1 !MODIFY THE LOOP LIMIT TO RUN A EXTRA TIME

5 DO SOMETHING

6 GOTO 8

7 DO SOMETHING DIFFERENT

8 NEXT A

What i want is a loop that changes itself to run extra times if needed, based on whether a certain conditional variable is 1 or 0.

I am fairly certain something like this can be done in languages like C, but is it possible in Basic/XB?

No need to modify z. For an extra blast around the loop just decrement a by one. Though what you have done looks okay to me. Both a and z will be evaluated by NEXT. Edited December 22, 2017 by Willsy