# C Program for Extended Euclidean algorithms?

CServer Side ProgrammingProgramming

Here we will see the extended Euclidean algorithm implemented using C. The extended Euclidean algorithm is also used to get the GCD. This finds integer coefficients of x and y like below −

𝑎𝑥+𝑏𝑦 = gcd(𝑎,𝑏)

Here in this algorithm it updates the value of gcd(a, b) using the recursive call like this − gcd(b mod a, a). Let us see the algorithm to get the idea

## Algorithm

### EuclideanExtended(a, b, x, y)

begin
if a is 0, then
x := 0
y := 1
return b
end if
gcd := EuclideanExtended(b mod a, a, x1, y1)
x := y1 – (b/a)*x1
y := x1
return gcd
end

## Example

Live Demo

#include <stdio.h>
int EuclideanExtended(int a, int b, int* x, int* y) {
if (a == 0) {
*x = 0;
*y = 1;
return b;
}
int xtemp, ytemp; // To store results of recursive call
int res = EuclideanExtended(b % a, a, &xtemp, &ytemp);
*x = ytemp - (b / a) * xtemp;
*y = xtemp;
return res;
}
int main() {
int x, y;
int a = 60, b = 25;
int res = EuclideanExtended(a, b, &x, &y);
printf("gcd(%d, %d) = %d", a, b, res);
}

## Output

gcd(60, 25) = 5
Published on 26-Jul-2019 12:28:54