Access array without a for loop?

[amz_best]

What is it you are trying to achieve?
Access an array without a for loop


What is the problem you are having?
idk how 2.


Describe what you have tried to solve this problem
tried not using a for loop. didnt work.


Post any relevant code (You may choose to attach the file instead of posting the code if it is too long)
nothing relevant, i just need the basic idea

Turing:

<Add your code here>

Please specify what version of Turing you are using
latest version of open turing

[Tony]

amz_best @ Sat Sep 27, 2014 3:38 pm wrote:

tried not using a for loop. didnt work.

Lets see how you've tried it. While at it, post an example that _does_ use a loop as well -- this can be used to figure out parts that are necessary, and what can be taken out.

[Nathan4102]

If you want to iterate through the entirety of an array, you need a for loop.

If you want to access a specific index of an array, you can get away with no for loop.

Whether in a for loop or not in a for loop, the array-access code syntax is identical.

[Raknarg]

@nathan technically you don't need a for loop, per se...

[Tony]

or a loop at all. E.g. recursion or https://en.wikipedia.org/wiki/Loop_unrolling

[Raknarg]

How would you do it with recursion?

[Tony]

writing loops using recursive calls

Quote:

$ irb
2.1.2 :001 > def go(arr)
2.1.2 :002?> if arr.any?
2.1.2 :003?> puts "item #{arr.first}"
2.1.2 :004?> go(arr[1..-1])
2.1.2 :005?> end
2.1.2 :006?> end
=> :go
2.1.2 :007 > go([1,2,3])
item 1
item 2
item 3
=> nil

[amz_best]

can someone explain to me what this recursion idea is?

[Tony]

https://en.wikipedia.org/wiki/Recursion_(computer_science)

Quote:

Recursion in computer science is a method where the solution to a problem depends on solutions to smaller instances of the same problem

[wtd]

When you loop in a program, what you're really doing, however the code may express it, is setting an initial state, checking for a condition, performing some set of operations, then doing it all again.

We can do this with a for loop in C.

code:

int i; for (I = 0; I < 5; I++) {    printf("%d\n", I); }

And this will print the follow to stdout.

code:

0 1 2 3 4

But, a function can also create an initial state, it can test for a condition, and it can process a whole series of operations.

code:

void my_function(int i) {    if (i < 5) {       printf("%d\n", i);    } }

And if we call the function again it can also repeat this.

code:

void my_function(int i) {    if (i < 5) {       printf("%d\n", i);       my_function(i + 1);    } }

Such that the following will replicate the original for loop's effects.

code:

my_function(0);

[wtd]

Oh, oops... thought this was in C help. Ah well, concept is the same.

[Dreadnought]

Here's the translation into Turing.

wtd wrote:

When you loop in a program, what you're really doing, however the code may express it, is setting an initial state, checking for a condition, performing some set of operations, then doing it all again.

We can do this with a for loop in C [Turing].

Turing:

for i : 0 .. 4     put i end for

And this will print the following to stdout [the run window in Turing].

code:

0 1 2 3 4

But, a function[a function that does not return a value is a procedure in Turing] can also create an initial state, it can test for a condition, and it can process a whole series of operations.

Turing:

procedure my_procedure (i : int)     if (i < 5) then         put i     end if end my_procedure

And if we call the function again it can also repeat this.

Turing:

procedure my_procedure  (i : int)     if (i < 5) then         put i         my_procedure (i + 1)     end if end my_procedure

Such that the following will replicate the original for loop's effects.

Turing:

my_procedure (0)