recursion

This is a discussion on recursion within the C++ Programming forums, part of the General Programming Boards category; Can someone please explain recursive to me?! I know that recursion is a function calling itself, but when it says ...

  1. #1
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    recursion

    Can someone please explain recursive to me?! I know that recursion is a function calling itself, but when it says
    n = 4
    Code:
    int funt1 (int n)
    {
    if (n == 0)
    {
    return 1;
    }
    else
    {
    Return 2* funt1 (n-1);
    }
    I think thats right. Im doing it by memory.
    I am trying to write a program that takes a user input number and change the number into binary, octal, and the other one...lol. Its gotta have a class, a stack, and recursion.

  2. #2
    and the hat of wrongness Salem's Avatar
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    > I think thats right. Im doing it by memory.
    Well post what you actually tried then.
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
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  3. #3
    Registered User Ephraim's Avatar
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    first call:
    Code:
    funt1(4)
    Inside there:
    Code:
    funt1(4) calls -> funt1(4-1) calls -> funt1(3-1) calls -> funt1(2-1) calls -> funt1(1-1)
    now we are at the special point with n == 0 (remember your if(n == 0) )
    so the function returns a 1.
    and every time it returns it will be multiplied by 2.
    Code:
    funt1(4) -> funt1(4-1) -> funt1(3-1) -> funt1(2-1) -> funt1(1-1)
    16 <- 2*       <- 2*         <- 2*         <- 2*         <- 1
    so you will get 2^4 which is16.

    Hope it helped you

    Ciao Ephraim

  4. #4
    Registered User major_small's Avatar
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    ooh yay... another excuse to write a recursive function:
    Code:
    double power(int num,int exp);
    ...
    double power(int num, int exp)
    {
       if(exp==0)
          return 1;
       else if(exp>1)
          return (num*power(num,exp-1));
       else
          return num;
    }
    it goes all the way in, and when exp becomes 1, it returns num, which is multiplied by num and returned to the parent, which is multiplied by num and returned to the parent, which is...
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  5. #5
    Registered User Ephraim's Avatar
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    Code:
    double power(int num, int exp)
    {
       if(exp==0)
          return 1;
       else if(exp>1)
          return (num*power(num,exp-1));
       else
          return num;
    }
    Tricky but for what reason do you have the
    if(exp == 0) there. You will never go into this section
    If Exp == 1 it not calls again the power but returns num.
    and so the exp isn't subtracted by -1, so never come into
    exp==0 section

    just kidding
    I like this way of programming, so the brain can get really f*****

    Ciao Ephraim
    Last edited by Ephraim; 03-03-2004 at 09:22 AM.

  6. #6
    Registered User major_small's Avatar
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    there's no trick there... what is X^0?

    this doesn' handle negative exponents well though...
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  7. #7
    Registered User Ephraim's Avatar
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    jep you are right
    Forgotten this point.
    and with the negative thing ...
    I think you can just use an unsigned int as exp isn't it?!

    Ciao Ephraim

  8. #8
    Registered User major_small's Avatar
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    you could cast the exponent to an unsigned int, but what if they want to find out what x^-y is? they couldn't use this function (without modification) for it...
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