codice:
char buffer[11]="\0";
unsigned int year;
unsigned int month;
unsigned int day;
//vengono valorizzati day, month e year...
year=2006;
month=12;
day=19;
//Controlli di base
if (year>9999 || year<1 || month>12 || month<1 || day>31 || day<0)
{
    printf("Errore: dati non validi.");
    return 1; //Supponendo di essere in main().
}
itoa(day,buffer,10);
buffer[2]='/';
itoa(month,buffer+3,10);
buffer[5]='/';
itoa(year,buffer+6,10);
printf(buffer);