RE: C++ Recursive Functions
- From: "Ken Perry" <whistler@xxxxxxxxxxxxx>
- To: <programmingblind@xxxxxxxxxxxxx>
- Date: Tue, 13 Nov 2007 23:27:41 -0800
In your recursive function you did not return a value for your else
statement you just killed it which is very bad. You should have done in
your else
return (gcd (r, bla));
If you make that a return rather than just a function call your program
should work.
Ken
-----Original Message-----
From: programmingblind-bounce@xxxxxxxxxxxxx
[mailto:programmingblind-bounce@xxxxxxxxxxxxx] On Behalf Of Jared Wright
Sent: Tuesday, November 13, 2007 8:27 PM
To: programmingblind@xxxxxxxxxxxxx
Subject: C++ Recursive Functions
Hi there everyone, Well, I've hit a snag on an assignment for my C++ course.
We are to use recursion to find the GCD (greatest common
divisor) of two integers. The program will eventually progress to generating
random numbers and using alternate algorithms (with counters to see which
require more recursive function calls) but that's neither here nor there for
the moment.
Within the main function, a call is made to the GCD function, giving it
two integer parameters to work with (call them q and r).
If r = 0, the function returns q. If not, the function calls itself again
using the parameters r and q%r. Eventually the second integer should be 0,
and the first integer should be the GCD I'm looking for. If I manually input
0 as the second integer in the initial function call, everything works fine.
But if recursion has to be utilized, I always get a return value of 136136,
regardless of what the input values are. I think I might be pointing
somewhere incorrectly, but I can't spot it and don't have the knowledge to
say for sure that's even the problem. Any guidance is appreciated. The
relevant code is below for your perusal.
Thanks in advance.
JW
#include <iostream>
using namespace std;
int gcd(int, int); // Declare GCD function.
int main ()
{
int q(0), r(0), temp(0); // Declare main function's variables and create
temp variable.
cout << "Please enter two numbers whose GCD is to be found.\nPress enter
after inputting the first number,
then enter the second and press enter again.\n";
cin >> q >> r;
if (r > q) {
temp = q;
q = r;
r = temp; // This is for an instance where the first number is
smaller than the second.
}
cout << "The greatest common divisor of " << q << " and " << r << "
is " << gcd(q, r) << ".\n"; // Here is the function call that keeps
returning 136136.
return 0;
}
int gcd(int q, int r) // GCD function definition begins here.
{
if (r == 0)
return q;
else
gcd(r, q%r); // And this is where the recursion is, and I think the
trouble is somewhere around here.
}
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