Eu stiu ca nu conteaza, sunt la fel de rapide.
# include <cstdio>
int a, b;
int main (void) {
freopen ("adunare.in", "r", stdin); // deschide in mod citire --- stdin + "r"
freopen ("adunare.out", "w", stdout);// in mod afisare -- stdout + "w"
scanf ("%d %d", &a, &b); // observi, scanf nu fscanf, ca si la citirea de la tastatura
printf ("%d", a + b); // la fel, ca si afisarea pe ecran
fclose (stdin), fclose (stdout);
}