/* * File: euclid.c * -------------- * This program computes a greates common divisor using * Euclid's algorithm. */#include <stdio.h>#include "genlib.h"#include "simpio.h"/* Function prototypes */int GCD(int x, int y);/* Main program */main(){    int x, y;    printf("This program calculates greatest common divisors.\n");    printf("Enter two integers, x and y.\n");    printf("x = ? ");    x = GetInteger();    printf("y = ? ");    y = GetInteger();    printf("The gcd of %d and %d is %d.\n", x, y, GCD(x, y));}/* * Function: GCD * Usage: gcd = GCD(x, y); * ----------------------- * Returns the greatest common divisor of x and y, * calculated by Euclid's algorithm, which is discussed * as Proposition 7 in Book II of Euclid's Elements. */int GCD(int x, int y){    int r;    while (TRUE) {        r = x % y;        if (r == 0) break;        x = y;        y = r;    }    return (y);}