File Input Output sample program C/C++

#include <stdio.h>

int main ()
{
  freopen ("numbers.txt","r",stdin);
  freopen ("summation.txt","w",stdout);
  int a, b, sum;
  scanf("%d%d", &a, &b);
  sum = a+b;
  printf("%d\n", sum);
  return 0;
}