/* 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'; }