Referencing vector causes error when running program - c++

Question

I am trying to make a program that will take a users input to make multiple forms. I am stuck on trying to get the vector (that will be filled with objects of the form class that the user creates) to be use-able in other functions. When I use the address-of operator (&) it gives me this error when the program gets to letting the user input the data to the objects.
This is the screen capture of the program and the error.
#include "pch.h"
#include <iostream>
#include <string>
#include <vector>
using namespace std;
class Form {
public:
string Fname;
string Lname;
string City;
string Street;
string State;
string ZipCode;
};
void menuMain();
void menu1st(vector<Form> &Fvect);
void menu1st(vector<Form> &Fvect)
{
int MainM;
int n;
cout << "NEW FORM(s)" << endl;
cout << "Enter the number of forms you would like to make (Maximum of 5): "; cin >> n; cout << endl;
for (int i = 0; i < n; i++)
{
cout << "First Name: "; cin >> Fvect[i].Fname; cout << endl;
cout << "Last Name: "; cin >> Fvect[i].Lname; cout << endl;
cout << "City: "; cin >> Fvect[i].City; cout << endl;
cout << "Street: "; cin >> Fvect[i].Street; cout << endl;
cout << "State: "; cin >> Fvect[i].State; cout << endl;
cout << "Zip Code: "; cin >> Fvect[i].ZipCode; cout << endl;
}
cout << "Enter 1 to go back to main: "; cin >> MainM;
if (MainM == 1)
{
menuMain();
}
else
{
cout << "Error not a correct input." << endl;
}
}
void menu2nd()
{
int MainM;
//int Fnum;
vector<Form> Fvect;
cout << "EDIT A FORM" << endl;
cout << Fvect[1].Fname;
cout << "Enter the ";
cout << "Enter 1 to go back to main: "; cin >> MainM;
if (MainM == 1)
{
menuMain();
}
else
{
cout << "Error not a correct input." << endl;
}
}
void menuMain()
{
int Pnum;
cout << "INFORMATION FORMATTING PROGRAM" << endl;
cout << "1. Create new form's." << endl;
cout << "2. Edit a form." << endl;
cout << "3. Print forms." << endl;
cout << "4. Erase a form." << endl;
cout << "5. Exit Program." << endl;
cout << "Enter the action you want to take (1-5): "; cin >> Pnum;
vector<Form> Fvect;
if (Pnum == 1)
{
menu1st(Fvect);
}
if (Pnum == 2)
{
menu2nd();
}
else
{
cout << "Error not a correct input." << endl;
}
}
int main()
{
menuMain();
}

Answer 1

You are accessing Fvect using an invalid index in the following lines:
cout << "First Name: "; cin >> Fvect[i].Fname; cout << endl;
cout << "Last Name: "; cin >> Fvect[i].Lname; cout << endl;
cout << "City: "; cin >> Fvect[i].City; cout << endl;
cout << "Street: "; cin >> Fvect[i].Street; cout << endl;
cout << "State: "; cin >> Fvect[i].State; cout << endl;
cout << "Zip Code: "; cin >> Fvect[i].ZipCode; cout << endl;
Consequently, your program has undefined behavior.
You need to have items in a std::vector before you can access an item from it using the array syntax. What you need to do is:
Read the data to an object of type Form.
Add the object to the std::vector.
Replace those lines with:
Form form;
cout << "First Name: "; cin >> form.Fname; cout << endl;
cout << "Last Name: "; cin >> form.Lname; cout << endl;
cout << "City: "; cin >> form.City; cout << endl;
cout << "Street: "; cin >> form.Street; cout << endl;
cout << "State: "; cin >> form.State; cout << endl;
cout << "Zip Code: "; cin >> form.ZipCode; cout << endl;
Fvect.push_back(form);
PS
I am not sure why you have the cout << endl; in those lines. You don't need them. It will be sufficient to use:
cout << "First Name: "; cin >> form.Fname;
cout << "Last Name: "; cin >> form.Lname;
cout << "City: "; cin >> form.City;
cout << "Street: "; cin >> form.Street;
cout << "State: "; cin >> form.State;
cout << "Zip Code: "; cin >> form.ZipCode;