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Increase integer variable
Posted: 7 Apr 2014 13:17
by Eftychios
Hello,
if i have an integer variable Counter = 100
and i want this variable to make it + 1 so the new one will be 101. How can i do this?
In java we can write Counter = Counter + 1;
To be more specific i have made something like this
Code: Select all
for each Counter = std::downTo(20, 1) do
if Button:getLabel <> "Number" then
%do some things here
else
Counter = Counter + 1 <----- What i want to do is if the label is equals to something then to try
again without decrease the counter.
end foreach.
Thanks in advance.
Posted: 8 Apr 2014 6:42
by Tonton Luc
Hi,
You can use this :
Code: Select all
facts
counter:interger:=erroneous.
goal
counter := 100,
foreach _Cpt = std::fromTo(0,10) do
stdio::write(counter),stdio::nl,
counter := counter + 1
end foreach,
Posted: 8 Apr 2014 8:53
by Eftychios
Thank you very much .... it works fine :)
Posted: 8 Apr 2014 15:43
by Thomas Linder Puls
In general you should write your algorithms in a way which does not need such mutable variables, for example by using recursion instead of foreach.
Butt there are situations where you may want to have such side effects anyway. In such cases, you should
not use a fact variable as suggested by Tonton Luc (sorry, TonTon
). Facts should be used to hold the state of your program, not to be temporaries for algorithms.
A much better solution is to use a
varM:
Code: Select all
goal
Counter = varM::new(100),
foreach _Cpt = std::fromTo(0,10) do
stdio::write(Counter:value), stdio::nl,
Counter:value := Counter:value + 1
end foreach.
But as mentioned you should perhaps rather use a recursive predicate (even if the code looks more difficult):
Code: Select all
clauses
something(N, Cnt1) = Cnt0 :-
if N = 0 then
Cnt0 = Cnt1
else
if test(...) then
% some code
Cnt2 = Cnt1
else
Cnt2 = Cnt1+1
end if,
Cnt0 = something(N-1, Cnt2)
end if.
Posted: 9 Apr 2014 6:51
by Tonton Luc
Ok, thanks Thomas.
I did not know that varM was better in this case.
Posted: 9 Apr 2014 14:19
by Harrison Pratt
Question for Thomas:
Is this somewhat equivalent code compiled to better/worse/same code as the if/then/else syntax?
Code: Select all
something(0, Cnt) = Cnt :- !.
something(N, Cnt1) = Cnt0 :-
0 = N mod 2 , % if test(...) then
!,
Cnt0 = something( N-1, Cnt1 ).
something(N, Cnt) = Cnt0 :-
Cnt0 = something( N-1, Cnt + 1 ).
I find the if/then/else syntax to be visually bulky and harder to debug for more complex code, but of course that's just personal preference.
Disclaimer: code compiled but was not tested.
Posted: 9 Apr 2014 18:05
by Thomas Linder Puls
Choosing between if-then-else and backtracking+cut is more free. I/we do however use if-then-else more and more. The flow in if-then-else is clear and clean. Backtracking can be more complex, running a little several clauses:
Code: Select all
clauses
p(X) :-
X > 10,
pp1(X),
X < 20,
!,
pp2(X).
p(X) :-
pp3(X),
X < 30,
!,
pp4(X).
p(X) :-
pp5(X).
The code above is "silly", trying to rephrase it using if-then-else is quite difficult (which kind of prove that the code is "silly"). A potential problem with backtracking+cut is that code as above can evolve over time (during maintenance).
Posted: 9 Apr 2014 23:17
by Harrison Pratt
Thanks, Thomas. I understand your meaning.
Code maintainability (by ordinary mortals) and clarity should be the first consideration.