Recursion vs multiple functions

This is a discussion on Recursion vs multiple functions within the C++ Programming forums, part of the General Programming Boards category; Just a quick question on recursion. Does it make a difference in terms of speed/resourses/memory/whatever if one uses recursion instead ...

  1. #1
    Cheesy Poofs! PJYelton's Avatar
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    Recursion vs multiple functions

    Just a quick question on recursion. Does it make a difference in terms of speed/resourses/memory/whatever if one uses recursion instead of multiple functions if they both do the same thing? Like for example in this example:
    Code:
    // if one assumes x is 2
    int recursiveFunc(int x)
    {
       if (x==0)
         return 0;
       else
         return recursiveFunc(x-1);
    }
    versus
    Code:
    // if one assumes x is 2
    int func1()
    {
        return func2();
    }
    int func2()
    {
        return func3();
    }
    int func3()
    {
       return 0;
    }
    I agree that this is a stupid useless example, but it was the first thing that came to mind

    Both examples do the same thing, but aside from readability and the fact that the recursive one works for more values of x, is one of these faster/better than the other? I'm just not sure if the computer treats recursion as just another function call or if something different is done. Hope this makes sense...

  2. #2
    geek SilentStrike's Avatar
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    It's just another function all. The calling method is general enough so that it doesn't matter which function is called from which function.

    The recursive code with x = 2 will end up having to do a check to stop the recursion, while the non-recursive function can tell how many more functions to call, which favors the non-recursive function. However, the recursive function exist only once in the binary, while func1, func2, and func3 all exist in the binary causing it to be larger than just, say, having func1.

    Generally, I'd say just use whatever produces code that is easier to follow. If it happens to be recursion, use it, if it happens to be iteration, use it. Unless it's too slow, leave it there.
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  3. #3
    Programming Sex-God Polymorphic OOP's Avatar
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    No. All a function call does is toss data on the stack and jumps to some code -- whether you are calling the same function or a different one it does exactly the same thing. The question you probably should be asking is "is a loop better than recursion," which is "yes" in most cases... as long as it makes sense to do so.

  4. #4
    Guest Sebastiani's Avatar
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    Right. Generally, a recursive function will replace a loop and vice versa. The main consideration with recursion is how often will we recurse till we return from a call? The reason is, every time you enter the recursive function, variables in that function are created from the stack, and they won't be freed till the function returns, so that if we enter the recursion say, 100,000 times without returning even once, we have 100,000 copies of those variables, which obviously eats up the stack quite quickly. This would be the case for the recursion you gave, by the way. Other recursive functions, like quicksort, generally return from internal recursions quite frequently, and so are quite safe.



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  5. #5
    Cheesy Poofs! PJYelton's Avatar
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    Okay, thanks all. This is for a connect four AI I'm writing which looks 8 plys deep, but this takes up a bit of time with recursion and I wasn't sure if it would speed up if I made each level a different function unto its own.

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