/* 070903-5.c
* 30 min
*/
#include <stdio.h>
#include <string.h>
int Div9 (char *str);
void main (void)
{
char num [1025];
printf ("Introduce el número: ");
gets (num);
if (Div9(num)) printf ("%s es divisible por 9\n", num);
else printf ("%s no es divisible por 9\n", num);
}
int Div9 (char *str)
{
char num [1025];
int i, j, n;
int s;
do {
n = strlen (str);
j = 0;
for (i = 0; i < n; i+= 2) {
if (i == n - 1)
s = str [i] - '0';
else
s = str [i] - '0' + str [i+1] - '0';
if (s >= 10) {
num [j] = '1';
j++;
s -= 10;
}
num [j] = s + '0';
j++;
}
num [j] = '\0';
str = num;
} while (n > 1);
return num [0] == '9';
}