Cách ghi ra file txt với hàm ofstream trong C++?

Bạn nào giúp tớ sao ghi kết quả từ GTLN, GTNN, GTTB, kết quả từ tìm kiếm theo MSSV và tên SV ra file output.txt.

#include <cstdlib>
#include <iostream>
#include<stdio.h>
#include <fstream>
#include <cstring> 

const int MAX=50;
using namespace std;

struct sinhvien
{
    char mssv[8];
    float d,tb,max,min;
    char hoten[20];  
};

struct sinhvien sv[MAX];
void nhap(sinhvien sv[],int &n)
{
    do
    {
        cout<<"Moi nhap so luong sv: ";
        cin>>n;
        cout<<"Moi ban nhap thong tin ve sv: "<<endl;
        if (n<=0) cout << "Nhap sai! Hay nhap lai.
";
    } while (n<=0);
    cout<<endl<<"-------------------"<<endl;
    cout<<"NHAP DANH SACH SINH VIEN."<<endl;
    cout<<"========================="<<endl;
   
    for(int i=0;i<n;i++)
    {
        cout<<endl<<i+1<<". ";
        cout<<"Nhap ho va ten: ";
        cin>>sv[i].hoten;
        cout<<"   Nhap ma so sinh vien: ";
        cin>>sv[i].mssv;
        cout<<"   Nhap diem :";
        cin>>sv[i].d;
    }
    
    ofstream input ("input.txt",ios::out);
    input<<n<<endl;
     for(int i=0;i<n;i++)
     {
        input<<sv[i].hoten<<endl;
        input<<sv[i].mssv<<endl;
        input<<sv[i].d<<endl;
     }
     input.close();
}

void docfile(char tenfile[], sinhvien sv[], int &n)
{
     ifstream nhap(tenfile, ios::in);
     nhap>>n;
     for(int i=0;i<n;i++)
     {
        nhap>>sv[i].hoten;
        nhap>>sv[i].mssv;
        nhap>>sv[i].d;
     }
     nhap.close();
}

void xuat(sinhvien sv[],int n)
{
    cout<<"----------------------------
";
    cout<<" So luong hoc sinh la: "<<n<<endl;
    
    for(int i=0;i<n;i++)
    {
        cout<<i+1<<". ";
        cout<<"Ho ten : "<<sv[i].hoten<<" "<<"  Ma sv: "<<sv[i].mssv<<" "<<"  Diem la: "<<sv[i].d<<endl;
    }    
}


    // Tim so nho nhat

int timnhonhat( int n, sinhvien sv[MAX])
{
    int min=sv[0].d;
    for (int i=1; i<n; i++)
        if (min>sv[i].d) min=sv[i].d;
    return min;
}

    // Tim so lon nhat
int timlonnhat(int n, sinhvien sv[MAX])
{
    int max=sv[0].d;
    for (int i=1; i<n; i++)
        if (max<sv[i].d) max=sv[i].d;
    return max;
}

    // Tinh gia tri trung binh
double trungbinh(int n, sinhvien sv[MAX])
{
    long s=0;
    for (int i=0; i<n; i++)
        s = s + sv[i].d;
    return (double)s/n;
}

struct sinhvien timkiem(int n, sinhvien sv[MAX])
{
     struct sinhvien svTimThay;
    cout<<"
--------------------------
";
    cout<<"TIM KIEM THONG TIN SINH VIEN
";
       cout<<"----------------------------
";
       
       char mssv[8];
          cout<<("Ma so sinh vien can tim : ");
          fflush(stdin);
          gets(mssv);
        int timThay = 0;
          for (int i=0; i<n; i++)        
          {                                            // Neu Mssv nhap trung voi mssv cua sinh vien thu i
              if (strcmp(mssv,sv[i].mssv)==0)            // -> Tim thay.
             {
             svTimThay = sv[i];
             timThay = 1;
             break;
             }
            }
            cout<<"Ket qua tim kiem la: "<<endl<<endl;
            if (timThay==0)
            {
            cout<<"Khong tim thay sinh vien nao co ma la : "<<mssv;
              }
              else
              {
              cout<< "Ma so sinh vien la: "<< svTimThay.mssv<<endl;
              cout<< "Ten cua sinh vien la: "<< svTimThay.hoten<<endl;    
              cout<< "Diem cua sinh vien la: "<< svTimThay.d<<endl;
              }
        
        
        char hoten[20];
        cout<<"----------------------------
";
        cout<< "Ho va Ten can tim: ";
        fflush(stdin);
        gets(hoten);
          cout<< "Ket qua tim kiem la: "<<endl<<endl;
          for (int i=0; i<n; i++)
          {                                          // Neu Ten nhap trung voi Ten cua sinh vien thu i
             if (strcmp(hoten,sv[i].hoten)==0)      // -> Tim thay.
            {
            timThay = 1;
            cout<< "Ma so sinh vien la: "<< sv[i].mssv<<endl;
            cout<< "Ten cua sinh vien la: "<< sv[i].hoten<<endl;    
            cout<< "Diem cua sinh vien la: "<< sv[i].d<<endl;
             }
              }    
          if (timThay==0)
          {
            cout<<"Khong tim thay sinh vien nao co ten la :"<<hoten;
            }
}
void ketqua(char kq[], sinhvien sv[])
{
     ofstream output ("output.txt", ios::out);
     output.close();
}
int main(int argc, char *argv[])
{
    sinhvien sv[MAX];
    sinhvien svTimThay;
    int n;
    cout<<"Chao mung ban da dung chuong trinh."<<endl;
    //nhap(sv,n);
    //cout<<"Da luu danh sach sinh vien vao tep input.txt"<<endl;
    char tenfile[]="input.txt";
    docfile(tenfile,sv,n);
    cout<<"Xuat danh sach sinh vien tu input.txt "<<endl<<endl;
    xuat(sv,n);    
    cout<< "Gia tri nho nhat la: ";
    cout<< timnhonhat(n, sv) << endl;
    cout<< "Gia tri lon nhat la: ";
    cout<< timlonnhat(n, sv) << endl;
    cout<< "Gia tri trung binh cua cac phan tu la: ";
    cout<< trungbinh(n, sv) << endl;
    svTimThay=timkiem(n, sv);

    system("PAUSE");
    return EXIT_SUCCESS;
}