Contestcen@aol.com wrote:
GPC accepts the following program, but produces quite silly results:
program Foo;
var a: array [1 .. 2] of Integer value (0, 0); i: Integer;
begin i := 1; for a[i] := 1 to 10 do begin WriteLn (i, ' ', a[i]); if a[i] = 5 then i := 2 end end.
The problem is that it evaluates the index i each time, not once before the loop. It would be possible to fix it, but do we really want that? Neither BP nor CP/EP allow it, they allow only identifiers in for-loops.
Waldek and I see no need for such a feature.
Neither do I.
Nor I. I vaguely recall that it is forbidden in at least ISO 7185, but cannot quote chapter and verse. This is a milestone, where BP is more standards adherent :=)
I have come in late to this discussion, and I am not sure what is the supposed "misfeature." Are the participants saying that Borland Pascal does not accept an array element as the control variable of a For loop, and that therefore GPC should not accept array elements either?
If that is the case, then the premise is incorrect. BP does accept array elements as control variables. The following program compiles and runs correctly in BP. It produces the expected result 100.000.
Indeed, BP seems to allow constant array indices. :-(
It doesn't allow variable indices, as in the example above. At least, this avoids the really silly/dangerous cases. However, emulating BP's behaviour will be more tricky for us (I'll try to, but with dialect warnings).
Program Try; Var a: array[1..10] of integer; s: real; Begin {Try} s := 0.0; for a[1] := 1 to 10 do for a[2] := 1 to 10 do s := s + 1.0; writeln (s:10:3); End. {Try}
Using array elements as control variables is very useful when you want the ability to stop a deeply nested loop, checkpoint the program, and then resume the execution from the same point later. I would not like to see this capability removed.
As first glance, since only constant indices are allowed, it would seem to be equivalent to using a1, a2, ... instead of a[1], a[2], or am I missing something?
Can you give an example for the situation you describe?
Frank