I am in a beginner C++ class and I have a homework problem where I must to find the greatest common divisor through subtraction. I am totally lost. Can anyone show me what I am doing wrong?

#include <iostream>
using namespace std;


int main ()
{
int m;
int n;
int firstNum = m;
int secondNum = n;



cout << "1st number:" << endl;
cin >> firstNum;
cout << "2nd number:" << endl;
cin >> secondNum;

while (m != 0)
{


if (n > m )
{
int t = m; m = n; n = t;
}

m = n - m;

}

cout << "the gcd of" << endl;
cout << firstNum;
cout << "and" << endl;
cout << secondNum;
cout << "is" << endl;
cout << n;

return 0;
}

The traditional (if inefficient) algorithm is:

Thanks for the reply but I'm still confused

>Thanks for the reply but I'm still confused
Well, aside from spelling out the algorithm so that it's trivial to convert to C++, there's not much more I can do to help you. Search google for analyses on the algorithm. It's been around for a while, so you shouldn't have trouble finding anything.

Hi,

Ever tought about using the Algorithm of Euclides?

Example of getting the greatest common devider gcd(1147, 851)
Steps:
1) 1147 = 1x851 + 296
2) 851 = 2x296+259
3) 296 = 1x259 + 37
4) 259 = 7x37
Rest equals 0.
Then the gcd equals 37.

If you can translate this into C++ code, you should be able to find the solution.

If it's not clear, google for the Algorithm of Euclides!

The problem is I have to use this basic shell to get my answer. This is what I have so far. No matter what two numbers I enter I always get an answer of zero which is obviously not the gcd. I have spent hours trying to adjust it but I just can't get it to work. Any thoughts on a fix?

#include <iostream>
using namespace std;


int main ()
{
int m;
int n;
int firstNum;
int secondNum;


cout << "1st number:" << endl;
cin >> firstNum;
cout << "2nd number:" << endl;
cin >> secondNum;

m = firstNum;
n = secondNum;

while (m != 0)
{


if (n > m )
{
int t = m; m = n; n = t;
}

m = m - n;

}

cout << "the gcd of" << endl;
cout << firstNum;
cout << "and" << endl;
cout << secondNum;
cout << "is" << endl;
cout << m;

return 0;
}

>Ever tought about using the Algorithm of Euclides?
The pseudocode I gave was the Euclidean algorithm. It was an earlier formulation of the problem using subtraction instead of the later (more efficient) algorithm that uses the remainder of integer division.

>The problem is I have to use this basic shell to get my answer.
Then it's homework, and we won't do it for you. Unless you're incapable of doing simple math, it's a small step to convert the algorithm I gave you into something that fits your shell.

You can't give me a hint where my code goes wrong? It compiles and executes without any errors but I'm just not getting the right answer. Is the problem in my If statement?

i tried using your pseudocode and this is what I now have. It doesn't return any value. Any suggestions?

#include <iostream>
using namespace std;


int main ()
{
int m;
int n;
int firstNum;
int secondNum;


cout << "Enter 1st number:" << endl;
cin >> firstNum;
cout << "Enter 2nd number:" << endl;
cin >> secondNum;

m = firstNum;
n = secondNum;

while (m != n);
{
if (m > n)
m = m - n;
else
n = n - m;
}

return m;



cout << "the gcd of" << endl;
cout << firstNum;
cout << "and" << endl;
cout << secondNum;
cout << "is" << endl;
cout << m;

return 0;
}

Why do you return m after the loop??

There's no need to :!:

And look at your loop, look how you defined it :!: