c++ vector of structs inside class - c++

Question

hello all i am working on a school prject called inventory inquisitor. the specifications are as follows:
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so far i have created a class in which contains a struct and a vector of this struct.
all im trying to do so far is get the class to display the struct just to know it works but when i compile it and run it nothing happens. here is the code. excuse whatever rookie mistakes i have made i am very new with classes, and vectors. thanks you in advance!
//Inventory Inquisitor.cpp
#include <iostream>
#include <string>
#include <cctype> //for toupper
#include <fstream>
#include <vector>
using namespace std;
class Inventory
{
private:
struct item
{
string Description = " ";
double Quantity = 0;
double Wholesalescost = 0;
double Retailcost = 0;
string Dateadded = " ";
};
vector<item> Inv;
public:
void Display();
};
void Inventory::Display()
{
Inv[0].Description = "english";
Inv[0].Quantity = 1;
Inv[0].Wholesalescost = 100;
Inv[0].Retailcost = 200;
Inv[0].Dateadded = "3/8/2018";
cout << Inv[0].Description << endl;
cout << Inv[0].Quantity << endl;
cout << Inv[0].Wholesalescost << endl;
cout << Inv[0].Retailcost << endl;
cout << Inv[0].Dateadded << endl;
}
int main()
{
Inventory inst1;
inst1.Display();
}

Answer 1

You have to put something into the vector before accessing it:
// Create an item
item i;
i.Description = "english";
i.Quantity = 1;
i.Wholesalescost = 100;
i.Retailcost = 200;
i.Dateadded = 3/8/2018;
// The vector is empty, size() == 0
// Add it to the vector
Inv.push_back(i);
// Now the vector has 1 item, size() == 1
// Now you can print it
cout << Inv.at(0).Description << endl;
cout << Inv.at(0).Quantity << endl;
cout << Inv.at(0).Wholesalescost << endl;
cout << Inv.at(0).Retailcost << endl;
cout << Inv.at(0).Dateadded << endl;
According to your assignment, you will most likely change to function to print an existing item. You will have another function to add items to the vector.
void Inventory::Display(int index)
{
// Print an item already in the vector
if (index >= 0 && index < Inv.size()) {
cout << Inv.at(index).Description << endl;
cout << Inv.at(index).Quantity << endl;
cout << Inv.at(index).Wholesalescost << endl;
cout << Inv.at(index).Retailcost << endl;
cout << Inv.at(index).Dateadded << endl;
}
}