convert function into member function? - c++

Question

I'm new here and I'm looking for help with a program written in c++.
I want to convert following functions that are not in a class nor in main() of my program
void PrintInventory(vector<Item*> inventory);
vector<Item*> AddItemToInventory(vector<Item*> inventory);
vector<Item*> UpdateItemQtyInInventory(vector<Item*> inventory);
vector<Item*> RemoveItemFromInventory(vector<Item*> inventory);
into public function members of a class Inventory that have no parameters and return nothing.
I've been working on that for 4 days now and just can't figure out how I'm supposed to change these functions to be void and have no parameter without destroying the whole program...
If I go exactly by what the instruction say which is to make a void/no parameters out of the four functions, I would get something like:
class Inventory
{
public:
void PrintInventory() {}
void AddItemToInventory() {}
void UpdateItemQtyInInventory() {}
void RemoveItemFromInventory() {}
private:
vector<Item*> inventory;
};
Please give me a hint. I feel like the solution must be simple but I've been completely stuck for days.
Thanks for your help.
EDIT:
I'm still getting a bunch of errors and think I need to say a bit more about my code:
I have a base class Item and two derived classes Produce and Book. Then I have four function calls:
// Print all items in the inventory
void PrintInventory(vector<Item*> inventory);
// Dialogue to create a new item, then add that item to the inventory
vector<Item*> AddItemToInventory(vector<Item*> inventory);
// Dialogue to update the quantity of an item, then update that item in the inventory
vector<Item*> UpdateItemQtyInInventory(vector<Item*> inventory);
// Dialogue to remove a specific item, then remove that specific item from the inventory
vector<Item*> RemoveItemFromInventory(vector<Item*> inventory);
Next comes the main and my class Inventory that now has four converted functions with no return and no parameters that were not originally inside the class Inventory and had parameters/return before.
Here is the whole code, I think it's better to understand this way:
#include <iostream>
#include <string>
#include <vector>
#include <sstream>
#include <cstring>
using namespace std;
class Item {
public:
void SetName(string nm)
{
name = nm;
};
void SetQuantity(int qnty)
{
quantity = qnty;
};
void SetPrice(int prcInDllrs) //step1
{
priceInDollars = prcInDllrs; //step1
};
virtual void Print()
{
cout << name << " " << quantity << endl;
};
virtual ~Item()
{
return;
};
protected:
string name;
int quantity;
int priceInDollars; //step1
};
class Produce : public Item { // Derived from Item class
public:
void SetExpiration(string expir)
{
expiration = expir;
};
void Print()
{
cout << name << " x" << quantity
<< " for $" << priceInDollars //step1
<< " (Expires: " << expiration << ")"
<< endl;
};
private:
string expiration;
};
//step 2 add derived class Book
class Book : public Item { // Derived from Item class
public:
void SetAuthor(string authr) //create author function with parameter
{
author = authr;
};
void Print()
{
cout << name << " x" << quantity
<< " for $" << priceInDollars //step1
<< " (Author: " << author << ")"
<< endl;
};
private:
string author;
};
// Print all items in the inventory
void PrintInventory(vector<Item*> inventory);
// Dialogue to create a new item, then add that item to the inventory
vector<Item*> AddItemToInventory(vector<Item*> inventory);
// Dialogue to update the quantity of an item, then update that item in the inventory
vector<Item*> UpdateItemQtyInInventory(vector<Item*> inventory);
// Dialogue to remove a specific item, then remove that specific item from the inventory
vector<Item*> RemoveItemFromInventory(vector<Item*> inventory);
int main() {
vector<Item*> inventory;
string usrInptOptn = "default";
while (true) {
// Get user choice
cout << "\nEnter (p)rint, (a)dd, (u)pdate, (r)emove, or (q)uit: ";
getline(cin, usrInptOptn);
// Process user choice
if (usrInptOptn.size() == 0) {
continue;
}
else if (usrInptOptn.at(0) == 'p') {
PrintInventory(inventory);
}
else if (usrInptOptn.at(0) == 'a') {
inventory = AddItemToInventory(inventory);
}
else if (usrInptOptn.at(0) == 'u') {
inventory = UpdateItemQtyInInventory(inventory);
}
else if (usrInptOptn.at(0) == 'r') {
inventory = RemoveItemFromInventory(inventory);
}
else if (usrInptOptn.at(0) == 'q') {
cout << "\nGood bye." << endl;
break;
}
}
return 0;
}
class Inventory {
public:
void PrintInventory() {
unsigned int i = 0;
if (inventory.size() == 0) {
cout << "No items to print." << endl;
}
else {
for (i = 0; i<inventory.size(); ++i) {
cout << i << " - ";
inventory.at(i)->Print();
}
};
}
void AddItemToInventory() {
Produce* prdc;
Book* book; //create new pointer object of class book
string usrInptName = "";
string usrInptQntyStr = "";
istringstream inSS;
int usrInptQnty = 0;
string usrInptExpr = "";
int usrInptPrc = 0; //step1
string usrInptAuthr = ""; //declare variable
string usrInptBookName = "";
int usrInptQntyBook = 0;
string usrInptQntyBookStr = "";
string usrInptChoice = " ";
//loop user choice and ask again if choice is not valid
do {
cout << "Enter choice of adding (b)ook or (p)roduce: ";
getline(cin, usrInptChoice);
if (usrInptChoice != "b" && usrInptChoice != "p") {
cout << "Invalid Choice" << endl;
}
} while (usrInptChoice != "b" && usrInptChoice != "p");
//only ask for inventory type accoring to user input p or b
if (usrInptChoice == "p") {
cout << "Enter name of new produce: ";
getline(cin, usrInptName);
cout << "Enter quantity: ";
getline(cin, usrInptQntyStr);
inSS.str(usrInptQntyStr);
inSS >> usrInptQnty;
inSS.clear();
cout << "Enter expiration date: ";
getline(cin, usrInptExpr);
cout << "Enter the price per item : $"; //step1
cin >> usrInptPrc; //step1
prdc = new Produce;
prdc->SetName(usrInptName);
prdc->SetQuantity(usrInptQnty);
prdc->SetExpiration(usrInptExpr);
prdc->SetPrice(usrInptPrc);
inventory.push_back(prdc);
}
if (usrInptChoice == "b") {
cout << "Enter name of new book: ";
getline(cin, usrInptBookName);
cout << "Enter quantity: ";
getline(cin, usrInptQntyBookStr);
inSS.str(usrInptQntyBookStr);
inSS >> usrInptQntyBook;
inSS.clear();
cout << "Enter author: ";
getline(cin, usrInptAuthr);
cout << "Enter the price per item : $"; //step1
cin >> usrInptPrc; //step1
book = new Book;
book->SetName(usrInptBookName);
book->SetQuantity(usrInptQntyBook);
book->SetAuthor(usrInptAuthr);
book->SetPrice(usrInptPrc);
inventory.push_back(book);
};
}
void UpdateItemQtyInInventory() {
string usrIndexChoiceStr = "";
unsigned int usrIndexChoice = 0;
istringstream inSS;
string usrInptQntyStr = "";
int usrInptQnty = 0;
if (inventory.size() == 0) {
cout << "No items to update." << endl;
}
else {
PrintInventory();
do {
cout << "Update which item #: ";
getline(cin, usrIndexChoiceStr);
inSS.str(usrIndexChoiceStr);
inSS >> usrIndexChoice;
inSS.clear();
} while (!(usrIndexChoice < inventory.size()));
cout << "Enter new quantity: ";
getline(cin, usrInptQntyStr);
inSS.str(usrInptQntyStr);
inSS >> usrInptQnty;
inSS.clear();
inventory.at(usrIndexChoice)->SetQuantity(usrInptQnty);
};
}
void RemoveItemFromInventory() {
istringstream inSS;
string usrIndexChoiceStr = "";
unsigned int usrIndexChoice = 0;
string usrInptQntyStr = "";
if (inventory.size() == 0) {
cout << "No items to remove." << endl;
}
else {
PrintInventory();
do {
cout << "Remove which item #: ";
getline(cin, usrIndexChoiceStr);
inSS.str(usrIndexChoiceStr);
inSS >> usrIndexChoice;
inSS.clear();
} while (!(usrIndexChoice < inventory.size()));
inventory.erase(inventory.begin() + usrIndexChoice);
};
}
private:
vector<Item*> inventory;
};
I don't get any compilation errors in Visual Studio but when I try to build, there are 5 errors. Compiling the program in Geany gives me no errors either but when I build, it says:
undefined reference to `PrintInventory(std::vector<Item*, std::allocator<Item*> >)'
undefined reference to `AddItemToInventory(std::vector<Item*, std::allocator<Item*> >)'
undefined reference to `UpdateItemQtyInInventory(std::vector<Item*, std::allocator<Item*> >)'
undefined reference to `RemoveItemFromInventory(std::vector<Item*, std::allocator<Item*> >)'
collect2.exe: error: ld returned 1 exit status
Compilation failed.
I feel like I'm missing some basic, simple thing but I just can't figure it out. The instruction is confusing to me when it says I have to convert the functions PrintInventory, AddItemToInventory, UpdateItemQtyInInventory,
and RemoveItemFromInventory into void/no parameters but which functions does it refer to? The four definition lines? The actual functions? Both? And what about the main and the other classes? Wouldn't I need to change things there as well?

Answer 1

I believe your code conversion is correct. Since 'Inventory vector' is a a member variable it can be accessed by all the other member function and can also be manipulated. This removes the requirement for passing vector as argument.
Now for returning the vector I would suggest adding a new "GetInventory()" method which returns the vector or take a reference to pass the vector.
Hope it helps.

Answer 2

Thanks to WhozCraig, my problem has been solved:
"The class definition of Inventory has to come before main() somehow. Move it above main() and it should work."

Answer 3

Basic testing:
Note, there are no pointers in here
void test()
{
class T_item
{
public:
string name;
int quantity;
int priceInDollars;
};
vector<T_item> inventory;
T_item temp;
//add item:
temp.name = "name1";
temp.quantity = 1;
temp.priceInDollars = 1;
inventory.push_back(temp);
temp.name = "name2";
temp.quantity = 2;
temp.priceInDollars = 2;
inventory.push_back(temp);
cout << "print:\n";
for each(T_item item in inventory)
{
cout << item.name << endl;
cout << item.quantity << endl;
cout << item.priceInDollars << endl << endl;
}
//modify item at index 1:
inventory[1].name = "modified";
//delete item at index 0:
inventory.erase(inventory.begin() + 0);
cout << "print again:\n";
for each(T_item item in inventory)
{
cout << item.name << endl;
cout << item.quantity << endl;
cout << item.priceInDollars << endl << endl;
}
}
int main()
{
test();
return 0;
}