Hi,
im lost and i need help writing a function gcd that returns the greatest common divisor of two integers and has to allow five sets of numbers to be input by the user.
this is what i have so far where i put /* is where i need help the most. if someone could also explain it to me that will also be very well appreciated. thank you in advance

<< moderator edit: added [code][/code] tags >>

i ll give u a fn or the gcd of 2 nos..

<< moderator edit: added [code][/code] tags and formatting; added missing semicolon >>

just call this fn for the first 2 nos.. then the gcd and the 3rd no. and then there gcd and the 4th no. and so on..
till all the nos are over.. u ll get ur final answer...

The original posting (minah1984) seems to be using the definition of gcd to find the gcd. That's not a bad idea. The one thing missing is that he/she doesn't know how to tell whether i is a common divisor of j and k or not. Here's how to do that: the expression

has the value 0 if i divides both j and k and a positive value otherwise. (I'm assuming i, j, and k are positive).

The response from shre86 is just the euclidian algorithm for the gcd. I can't resist showing you the recursive way to do that.

I edited my quote of your code to fix an error ("return gcd(...").

Ironically (and fortunately), this tail-recursive version will just get compiled (by any non-bad compiler) to the non-recursive version, similar to

But of course, the recursive drawing of the algorithm is much prettier :-)

i write (GCD) programming code for you in two ways. you check this and compare with your code
First:
// Header files
#include <iostream.h>
#include<conio.h>


void GCD(int, int); // Function prototype


int main()
{

int first; // integer variables first to store first number
int second; // integer variables second to store second number
cout<<"Enter two different positive numbers";
cin>>first>>second; // getting input from the user two integers through keyboard

GCD(first, second); //calling function GCD and passing two integer values
getche(); // get character function getch() used to hold console window
return 0;
} // end main

void GCD(int first, int second)
{

int remainder; // integer variables remainder to store remainder.

do {

if (first> second) // IF condition to check whether the first number is greater than second

{
remainder = first % second; // if first number is greater than second then dividing first number by second to get remainder.
if (!(remainder ==0)) // IF condition to check if remainder Not equal to zero.
first = remainder; // if remainder is not equal to zero then assigning remainder to first
}
else //Else
{
remainder = second % first; // second number is greater than first then dividing second number by first to get remainder.
if (!(remainder ==0)) // IF condition to check if remainder Not equal to zero.
second = remainder; // if remainder is not equal to zero then assigning remainder to second number
}

}while(remainder!=0); // loop continues untill remainder not equal to zero
if (first > second) // IF condition to check whether the first number is greater than second
{
cout<<"Greatest Common Diviser "<< second; // if first number is greater than second then displaying second number which is Greatest Common Diviser of two numbers.
}
else //else
{
cout<<"Greatest Common Diviser "<<first; // second number is greater than first then displaying first number which is Greatest Common Diviser of two numbers.
}

} // end GCD

Second Code:
// Header files

#include <iostream.h> // header file for input output streams
#include <conio.h> // header file for console input output

using namespace std;

// declares variables

int GCD (int n1, int n2);

main()

{
int num1, num2;

cout << "Enter two differnt positive numbers: ";

cin >> num1 >>num2; // getting input from the user through keyboard

cout << "Greatest Common Divisor: "

<< GCD(num1, num2) << endl; // displaying GCD calculated
getch();
}

int GCD (int n1, int n2)
{

int rem;

while (n2 != 0)

{
rem = n1 % n2;

n1 = n2;

n2 = rem;
}

return (n1);
}

What would you put in the if condition to see if both x and y are divisible by i ?

There is such thing as overcommenting, you know :-)

This is the correct code:

/* prototype for gcd */ = int GCD (int a, int b);

<< /* function call for gcd */<<"\n\n"; = << GCD(a, b) << "\n\n";

/*header for gcd */ = GCD(int x, int y);



All of the above is correct... all we need to figure out is the if statement to determine if both x and y are divisible by i..I could not figure that out...

I tried everything like if(x+y % i) but nothing worked can someone help??

if( /* condition to see if both x and y are divisible by i */ )-->Does anyone know how to do this?????? :o

The number B is divisible by C if the remainder from dividing B by C is zero. The % operator computes the remainder.

I think I've already answered this but I'll do it in more detail.

x is divisible by i if the remainder when x is divided by i is 0, that is, x is divisible by i if and only if x%i == 0. Likewise, y is divisible by i if nd only if y%i== 0. Now the sum of 2 non-negative numbers is 0 if and only if each is 0, so x and y are both divisible by i if and only if x%i+y%i == 0.