recursion help

This is a discussion on recursion help within the C++ Programming forums, part of the General Programming Boards category; Hi, I am trying to learn some recursion and I am having trouble following this simple program: #include <iostream> #include ...

  1. #1
    Unregistered
    Guest

    recursion help

    Hi, I am trying to learn some recursion and I am having trouble following this simple program:

    #include <iostream>
    #include <stdlib.h>
    using namespace std;

    void fun(int x);

    int main(void)
    {
    fun(3);

    }

    void fun(int x)
    {
    if (x != 1) {
    fun(x - 1); // fun calls fun
    cout << x << endl;
    }
    }

    The output is:

    2
    3

    This is my understanding:

    x=3: so is 3 !=1 true so fun(3-1) or fun(2)

    so is 2 !=1 true so fun(2-1) or fun(1)

    so is 1 !=1 false

    cout x (doesn't x=1 ??)

    and why are two numbers printed?

    I'm sure this is simple for many of you, but I am simple, and if you could break it down for me I would be grateful.

  2. #2
    Evil Member
    Join Date
    Jan 2002
    Posts
    638
    Your problem has nothing to do with recursion. The cout is part of the if block, and is not executed if x != 1.

  3. #3
    Registered User biosx's Avatar
    Join Date
    Aug 2001
    Posts
    230
    Code:
    #include <iostream> 
    #include <stdlib.h> 
    using namespace std; 
    
    void fun(int x); 
    
    int main(void) 
    { 
       fun(3); 
    } 
    
    void fun(int x) 
    { 
       if (x != 1) 
          fun(x - 1); // fun calls fun 
    
       cout << x << endl; 
    }
    That should work the way you want.

  4. #4
    Unregistered
    Guest
    Thanks for the replies.

    But what I would like to understand is why the output is:

    2
    3

    When I try to trace it on paper I can not get that output. I know it is right (obviously) but can someone explain it to me.

    Can you take me step by step through the logic of the program.

    Thanks for your time.

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