i wanna out put the maximum minimum and average score as a statistic category under the student ids and grades in the output file. how do i do that?

here is the code:

#include "stdafx.h"
#include <iostream>
#include <string>
#include <fstream>
#include <assert.h>

using namespace std;

int openfiles(ifstream& infile, ofstream& outfile);

void Size(ofstream&, int, string);

int main()
{
    int num_student = 4, count, length, score2, w[6];

    ifstream infile, curvingfile; char x;

    ofstream outfile; float score;

    string  key, answer, id;

    do {
        openfiles(infile, outfile);  // function calling

        infile >> key; // answer key

        for (int i = 0; i < num_student; i++) // loop over each student

        {
            infile >> id;

            infile >> answer;

            count = 0;

            length = key.size(); // length represents number of questions in exam from exam1.dat
                                 // size is a string function....

            Size (outfile, length, answer);

            for (int j = 0; j < length; j++) // loop over each question
            {
                if (key[j] == answer[j])

                    count++;
            }

            score = (float) count / length; 

            score2 = (int)(score * 100);

            outfile << id << "     " << score2 << "%";

            if (score2 >= 90)//<-----w[0]

                outfile << "A" << endl;

            else if (score2 >= 80)//<-----w[1]

                outfile << "B" << endl;

            else if (score2 >= 70)//<-----w[2]

                outfile << "C" << endl;

            else if (score2 >= 60)//<-----w[3]

                outfile << "D" << endl;

            else if (score2 >= 50)//<-----w[4]

                outfile << "E" << endl;

            else if (score2 < 50)//<-----w[5]

                outfile << "F" << endl;
        }
        cout << "Would you like to attempt a new trial? (y/n): ";

        cin >> x;

    } while (x == 'y' || x == 'Y');

    return 0;
}

int openfiles(ifstream& infile, ofstream& outfile)
{
    string name1, name2, name3, answerstring, curvedata;

    cin >> name1; name2; name3;
    if (name1 == "exit" || name2 == "exit" || name3 == "exit" ) return false;

    cout << "Input the name for the exam file: ";

    cin >> name1;

    infile.open(name1.c_str());

    infile >> answerstring;

    cout << "Input the name for the curving file: ";

    cin >> name2;

    infile.open(name2.c_str());

    infile >> curvedata;

    cout << "Input the name for the output: ";

    cin >> name3;

    outfile.open(name3.c_str());

    return true;
}

void Size(ofstream& outfile, int length, string answer)

{
    bool check;// extra answers, lesser answers...

    if (answer.size() > length)

    {
        outfile << "Unnecessary extra answers";
    }

    else if (answer.size() < length)

    {
        outfile << "The remaining answers are incorrect";
    }

    else { check = false; };
}

and how do i use assert for preconditions and post conditional functions? i dont understand this that well...