I'm not sure exactly what your problem is. I'm getting that you need some help with your output functions but beyond that I can't understand what you are asking.
void output(constchar name[], double average, ostream& os) // Print results
{
os << "\n\nInput your File Name : " << name << endl;
os << "The average : " << setw(8) << average<< endl;
//make a new text file here and store the output to the file, example 10.txt
//to print the previous text file just open the most recent made file.
}
void output(constchar name[], int highest, int lowest, ostream& os) // Print results
{
os << "Largest Number in File : " << setw(8) << highest << endl;
os << "Smallest Number in File: " << setw(8) << lowest << endl;
//make a new text file code here then store this output to it, example 9.txt.
//then if you want to get the previous output just open the file.
}