Additionner les chiffres d'un nombre...

int toChiffre( int nombre )
{
int temp;
temp = nombre;
while( temp%10 > 9 )
{
temp = (temp/10) + (temp%10);
}
return temp;
}

#include <stdlib.h>
#include <stdio.h>

int mod9(int x)
{
  int c, res = x;
  while (res > 9 )
    {
      res = 0;
      while ( x > 0)
 {
   c = x % 10 ;
   x = x / 10 ;
   res += c;
 }
      x = res;
    }
  return x;
}

unsigned int values[] = { 7, 12, 23, 271, 314, 1234567};

int main(int argc, char* argv[])
{
  int i;
  for( i=0 ; i< sizeof(values)/sizeof(unsigned int) ; i++)
    {
      printf("%d modulo 9 = %d | %d\n", values[i], mod9(values[i]), values[i] % 9);
    }
  return EXIT_SUCCESS;
}

johand@bata:~/src/CCM/C$ ./mod9 
7 modulo 9 = 7 | 7
12 modulo 9 = 3 | 3
23 modulo 9 = 5 | 5
271 modulo 9 = 1 | 1
314 modulo 9 = 8 | 8
1234567 modulo 9 = 1 | 1