void filesum()
{
   const int buf_size = 1000;
   int i, j, nfiles = 2;
   float val;
   float buf[buf_size];

   for (i = 0; i<buf_size; i++) buf[i] = 0;

   FILE *file;
   char line[20];

   for (i = 1; i<= nfiles; i++ ) {
      file = fopen(Form("file%d.txt",i),"r");
      j = 0;
      while (fgets(line,20,file)) {
         sscanf(&line[0]  ,"%g", &val);
         buf[j] = buf[j]+val;
         j++;
      }
      fclose(file);
   }

   FILE *fsum = fopen("filesum.txt","w");
   for (i=0; i<j; i++) fprintf(fsum,"%g\n", buf[i]);
   fclose(fsum);
}