Understanding Recursive Functions

Nexa · #1 18-Nov-2004, 17:23

I do not really understand what is being asked here, would anybody like to offer there help to help me understand this word problem. Any help would be appreciated.

The greatest common divisor of integers x and y is the largest interger that
evenly divides both x and y. Write a recursive function gcd that returns the
greatest common divisor of x and y, which is defined recursively as follows:
If y is equal to 0, then gcd(x,y) is x: otherwise gcd(x,y) is gcd(y, x % y),
where % is the modulus operator.

Thanks,

Nexa

dsmith · #2 18-Nov-2004, 20:09

HI Nexa. I get a kick out of recursive functions. A recursive function simply keeps calling itself in a nested fashion until something inside the function tells it to return.

This function can be coded quite easily based upon the given alogorithm:

CPP / C++ / C Code:

int gcd(int x, int y)
{
  if(y)
    return gcd(y, x%y);
  else
    return x;
}

You need to test that because I didn't

Also, I am leaving the commenting to you so you can figure out what is happening.

Nexa · #3 18-Nov-2004, 20:14

Thanks, dssmith, Any help at this point is better than no help.

Nexa · #4 18-Nov-2004, 22:49

Ahhhh!, Can you say hit a brick wall. I know I probably have something so simple that I am not seeing here, but truth is I am so lost right now. My text book it not offering much help.
Here is what I have so far, all I ask is how do I get my function to work correctly. When I run it, it completely skips my function and exits the program.

CPP / C++ / C Code:

#include <iostream>

using std::cout;
using std::endl;
using std::cin;

// function prototype that specifies default arguments
int gcd( int, int );

int main()
{

int number_1;
int number_2;

cout << "type in 1st number" << endl;
cin >> number_1;

cout << "type in 2nd number" << endl;
cin >> number_2;


return 0; 

}


int gcd(int x, int y)
{
  if(y)

    return gcd(y, x%y);

  else

    return x;
}

nkhambal · #5 19-Nov-2004, 03:29

I guess you forgot to call your function in main().

. Function needs to be called for its code to be executed. You also need to print the value returned by gcd() function in main()

Nexa · #6 19-Nov-2004, 12:51

Suppose you are correct, I got a little ahead of myself and for got to print my code to screen and call the function. See sometimes it takes others to see little things you are missing.

Thanks much!!!!

Nexa

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