want to use vector and hash table vector array

[Tanvi2992]

//
// main.cpp
// Final_project_part-1
// Created by Tanvi and Jessica on 20/11/20.
//

#include "header.hpp"
//bool isValidDate(int, int, int);
void insert_apartment_lease(); //function to write record in binary file
void display_apt_lease(int); //function to display account details given by user
void update_apartment_lease(int); //function to modify record of file
void delete_lease(int);//function to delete record of file
void search_apt(int);
void display_all_lease(); //function to display all account details
void intro();//introductory screen function

int main() {
intro();
vector <apartment> apt[100];
int hashTableSize=100;
int ch, n;
//apartment apt;

string labels[] = {"Error","Add Renter Information","Modify the Leasing Information","Close Leasing","Search apartment","Display Leasing information", "Exit"};
int num;
//string num= to_stro
int d;
for (;ch!=6;) {
for(int i = 1; i<7; i++){
cout << i <<". "<< labels[i] << endl;
}
cout<<"Enter your Choice: ";
cin>>ch;
switch (ch){
case 1:
//cout<<"Enter key to be inserted: "<<endl;
//cin>>n;
insert_apartment_lease();
break;
case 2:
cout<<"\n\tEnter The apartment No. : "; cin>>num;
update_apartment_lease(num);
break;
case 3:
cout<<"\n\tEnter The apartment No. : ";
cin>>num;
delete_lease(num);
break;
case 4:
cout<<"\n\tEnter the date to search :"; cin>>d;
search_apt(d);
break;
case 5:
display_all_lease();
break;
case 6:
cout << "Thank you so much for using this program Bye"<< endl;
cout << "EXIT from the Program" << endl;
break;
default:
cout<<"Error....Wrong Choice Entered"<<endl;
continue;
}//switch
} //do while loop end
return 0;
}

void insert_apartment_lease()
{
//apartment apt;
vector <apartment> apartment_vec[100];
apartment apt;
ofstream outFile;
outFile.open("apartment.txt",ios::app);
apt.add_apt();
outFile.write((char*)&apt, sizeof(apartment));
outFile.close();
}

void update_apartment_lease(int n)
{
bool found=false;
apartment apt;
fstream File;
File.open("apartment.txt",ios::in|ios::out);
if(!File)
{
cout<<"File could not be open !! Press any Key...";
return;
}
while(!File.eof() && found==false)
{
File.read((char*)&apt, sizeof(apartment));
if(apt.re_aptno()==n)
{
apt.show_apt_info();
cout<<"\n\nEnter the new apartment details "<<endl;
apt.modify_apt_info();
int pos=(-1)*static_cast<int>(sizeof(apartment));
File.seekp(pos,ios::cur);
File.write((char*)&apt, sizeof(apartment));
cout<<"\n\t Record Updated \n";
found=true;
}
}
File.close();
if(found==false)
cout<<"\n\t Record Not Found \n";
}

void delete_lease(int n)
{
apartment apt;
ifstream inFile;
ofstream outFile;
inFile.open("apartment.txt");
if(!inFile)
{
cout<<"File could not be open !! Press any Key...";
return;
}
outFile.open("Temp.txt");
inFile.seekg(0,ios::beg);
while(inFile.read((char*)&apt, sizeof(apartment)))
{
if(apt.re_aptno()!=n)
{
outFile.write((char*)&apt, sizeof(apartment));
}

}
if (apt.re_aptno()==n)
{
cout<<"\n\tRecord Deleted \n"<< endl;
}
else
{
cout<<"\n\tyou have entered wrong Apt Number \n"<<endl;
}
inFile.close();
outFile.close();
remove("apartment.txt");
rename("Temp.txt","apartment.txt");

}
void search_apt(int n)
{
apartment apt;
bool flag=false;
ifstream inFile;
inFile.open("apartment.txt");
if(!inFile)
{
cout<<"File could not be open !! Press any Key...";
return;
}
cout<<"\nAPARTMENT DETAILS\n";

while(inFile.read((char*)&apt, sizeof(apartment)))
{
if(apt.lease_date()==n)
{
apt.show_apt_info();
flag=true;
}
}
inFile.close();
if(flag==false)
cout<<"\n\nApartment number does not exist";
}

void display_all_lease()
{
apartment apt;
ifstream inFile;
inFile.open("apartment.txt");
if(!inFile)
{
cout<<"File could not be open !! Press any Key...";
return;
}
cout<<"\n\n\t\tAPARTMENT RENTER LIST\n\n";
cout<<"==========================================================\n";
cout<<"START_DATE END_DATE Apt no. NAME MONTHLY_RENT\n";
cout<<"==========================================================\n";
while(inFile.read((char*)&apt, sizeof(apartment)))
{
apt.report();
}
inFile.close();
cout << "\n" <<endl;
}

void intro()
{
cout<<"\nAPARTMENT LEASING";
cout<<"\n MANAGEMENT";
cout<<"\n SYSTEM";
cout<<"\nMADE BY : Tanvi and Jessica";
cout<<"\nSCHOOL : University of New Haven";
cout<<"\nSUBMITTED TO : Ms. Liberty Page"<<endl;
}

[salem c]

Edit your post for readability.
https://www.cplusplus.com/articles/jEywvCM9/

Where is header.hpp ?

You might want to delete or sanitise your intro function to have less personal information.

[seeplus]

vector <apartment> apt[100];

This probably doesn't do what you think it does. This defines an array apt of 100 elements with each element being of type vector<apartment>