Ackermann Function w/ a twist.

This is a discussion on Ackermann Function w/ a twist. within the C++ Programming forums, part of the General Programming Boards category; function header: void acker (int m, int n, int &result) There's no return type so I can't return things for ...

  1. #1
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    Ackermann Function w/ a twist.

    function header:

    void acker (int m, int n, int &result)

    There's no return type so I can't return things for each recursive call... Instead I need to use result somehow to hold the final value. This is the first time I've ever heard of the Ackermann function and I'm trying to wrap my head around how it works so I can figure out how to use result to get the final value.

    [edit] this is especially problematic if you consider that in the case that:

    for A(m,n)
    if m>0 AND n>0 then the call should look like:
    A(m-1, A(m,n-1))
    but if the return type is void I can't pass a void to a parameter that takes an int obviously...

    Right now, the call #s grow so large I'm not sure how to do it.

  2. #2
    "I Win!" by U. Lose vart's Avatar
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    if your problem is just return type write
    Code:
    int MyAcker(int m, int n)
    {
       int result =0;
       acker ( m,  n,  &result);
       return result;
    }
    and write your recursive code using this function instead
    To be or not to be == true

  3. #3
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    Quote Originally Posted by vart View Post
    if your problem is just return type write
    Code:
    int MyAcker(int m, int n)
    {
       int result =0;
       acker ( m,  n,  &result);
       return result;
    }
    and write your recursive code using this function instead
    I need to write it intentionally without the return type.

  4. #4
    C++ Witch laserlight's Avatar
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    Try writing it with an int return type first. Changing it to use the reference parameter as an out parameter is relatively easy.
    Quote Originally Posted by Bjarne Stroustrup (2000-10-14)
    I get maybe two dozen requests for help with some sort of programming or design problem every day. Most have more sense than to send me hundreds of lines of code. If they do, I ask them to find the smallest example that exhibits the problem and send me that. Mostly, they then find the error themselves. "Finding the smallest program that demonstrates the error" is a powerful debugging tool.
    Look up a C++ Reference and learn How To Ask Questions The Smart Way

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    Quote Originally Posted by laserlight View Post
    Try writing it with an int return type first. Changing it to use the reference parameter as an out parameter is relatively easy.
    Having no returns anywhere in the program is whats hanging me up, and the fact that you can't call it like you can with a return type because you can't make the call I noted in the original post when m & n are >0.

  6. #6
    "I Win!" by U. Lose vart's Avatar
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    Code:
    if(m> 0 && n > 0)
    { 
       int tempRes = 0;
       acker (m, n - 1, tempRes);
       acker (m-1, tempRes,result);
    }
    To be or not to be == true

  7. #7
    C++ Witch laserlight's Avatar
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    Quote Originally Posted by Sparrowhawk
    Having no returns anywhere in the program is whats hanging me up, and the fact that you can't call it like you can with a return type because you can't make the call I noted in the original post when m & n are >0.
    Compare:
    Code:
    int factorial(int n)
    {
        assert(n >= 0 && "Factorial operand must be non-negative.");
        if (n == 0)
        {
            return 1;
        }
        else
        {
            return n * factorial(n - 1);
        }
    }
    to:
    Code:
    void factorial(int n, int& result)
    {
        assert(n >= 0 && "Factorial operand must be non-negative.");
        if (n == 0)
        {
            result = 1;
        }
        else
        {
            int temp;
            factorial(n - 1, temp);
            result = n * temp;
        }
    }
    Quote Originally Posted by Bjarne Stroustrup (2000-10-14)
    I get maybe two dozen requests for help with some sort of programming or design problem every day. Most have more sense than to send me hundreds of lines of code. If they do, I ask them to find the smallest example that exhibits the problem and send me that. Mostly, they then find the error themselves. "Finding the smallest program that demonstrates the error" is a powerful debugging tool.
    Look up a C++ Reference and learn How To Ask Questions The Smart Way

  8. #8
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    Yeah I see where you're both going with this... and btw Vart you nailed it, that worked like a charm.

    I just need to think about it for awhile I guess. The whole using a temp variable thing is throwing me. It makes a new temp=0 everytime a new call is made where m & n are >0 from that original call... So is it just a way to make the call possible, or does it have other significance?

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