recursion question

This is a discussion on recursion question within the C Programming forums, part of the General Programming Boards category; This question concerns a recursive function i have to write. its basically has to take a number in that will ...

  1. #1
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    This question concerns a recursive function i have to write. its basically has to take a number in that will represent the the number of times you flip a coin. I need a way to print out all possible solutions.

    So for example say the user puts in 1, the output would be ' HT '.
    input is 2 so it prints hh tt th ht etc.

    What it does is takes in a number from the user and outputs the possible

    so far ive come up with
    Code:
    int coin(int x)
    {
    
    if(x==0)
    return;
    
    else
    {
    return coin(x-1);
    
    }
    QUESTION NOW IS:

    How would i print out the possible solutions. I was thinking something like strcat adding the letters but im not really sure how to proceed from where i am?
    Last edited by Salem; 10-06-2008 at 12:01 AM. Reason: Added code tags - learn to use them yourself

  2. #2
    and the Hat of Guessing tabstop's Avatar
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    I would suggest with, say, two coin flips and three coin flips. Look for patterns -- especially ways to use the two-coin-flip answers inside the three-coin-flip problem (since that's what recursion does, go down one level).

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    Quote Originally Posted by tabstop View Post
    I would suggest with, say, two coin flips and three coin flips. Look for patterns -- especially ways to use the two-coin-flip answers inside the three-coin-flip problem (since that's what recursion does, go down one level).
    ok. well correct me if i am wrong as i am just a begining comp science. student. I was informed that i had to do a double recursive call for this to even work period. I dont know if it makes sense at all. On the other hand how would i even go about coding something like this.

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    and the Hat of Guessing tabstop's Avatar
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    Quote Originally Posted by sumdude View Post
    I was informed that i had to do a double recursive call for this to even work period.
    If you mean your function will call function(n-1) twice, then yes. Most coins do have two sides.
    Quote Originally Posted by sumdude View Post
    I dont know if it makes sense at all. On the other hand how would i even go about coding something like this.
    That's why you start with paper. Write out the possibilities for two coins and three coins and look at the patterns.

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    ok will try that out. appreciate the help

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    This is what i came up with but it only prints the h's. any help?

    int flip(int x, char string[])
    {


    if(x==0)
    { printf("%s\n", string);
    return 0; }

    if(x>0)

    {


    return flip(x-1,strcat(string,"H"));
    return flip(x-1,strcat(string,"T"));


    }


    }
    Can someone tell me where im going wrong please/

  7. #7
    and the Hat of Guessing tabstop's Avatar
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    Once you hit return, that's it. There's no way to get to the line "return flip(x-1, strcat(string, "T"));" in this function.

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    Quote Originally Posted by tabstop View Post
    Once you hit return, that's it. There's no way to get to the line "return flip(x-1, strcat(string, "T"));" in this function.
    so how can i resolve this problem?

  9. #9
    and the Hat of Guessing tabstop's Avatar
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    Don't return.

    Just call the function.

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    ok here is what im getting

    Please enter number of flips
    2
    HTHH
    HTHHT
    HTHHTTH
    HTHHTTHT

    why is this happen. Also i did declare in main ..... char sting[50]="HT"

  11. #11
    and the Hat of Guessing tabstop's Avatar
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    Quote Originally Posted by sumdude View Post
    char sting[50]="HT"
    So don't do that. string must be empty when this function is first called.

    And as you can see, things are not getting removed when you go from the H call to the T call. I'm guessing you want to make two local copies of the string (one to be passed into the H call, one to be passed into the T call) so that they don't interfere with each other in this way.

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    still cant get this ting to work. now its begining to print out some wierd characters.

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