Example 5 at Library

gistfile1.cpp

#define MAX_INVENTORY 100
//Arguments to use in cin.ignore:
#define IGNORE_ARGS 256, '\n'


#include <fstream>
#include <iomanip>
#include <iostream>
#include <string>

using namespace std;

bool readInventory(string filename);

double checkout();

bool updateInventory(string filename);

struct Product
{
	int code; //Product code.
	string name; //Product name.

	double cost; //Product cost.

	bool byPounds; //By pounds (or by unit)
	
	//Union: Variables of the same type take up the same place in memory,
	//And since we don't access either of them at the same time, the code doesn't break.
	union
	{
		double pounds; //Pounds in inventory.
		int units; //Units in inventory.
	};

	//Normal if:
	//if (condition)
	// { code }
	//else { other code }
	//The inline if:
	//(condition ? code : other code)

	void print() //Print out this product.
	{
		cout	<< setw(8) << "Name:" << name << endl
				<< setw(8) << "Code:" << code << endl
				<< setw(8) << "Cost:" << cost << endl
				<< setw(8) << "By pounds:" << (byPounds ? "true" : "false") << endl
				<< setw(8) << (!byPounds ? "Units:" : "Pounds:") << (byPounds ? pounds : units) << endl;
	}
};



Product * inventory; //Pointer to first element in array of products.
int inventoryCount = 0;

Product * getProduct(int code);

int main()
{
	//1. Read in and store inventory.
	readInventory("items.txt"); //Read in the inventory from items.txt;
	
	double cost = checkout();
	cout << "Total cost: $" << setprecision(2) << fixed << cost << endl;
	//2. Get item code from user.
		//3. If valid
			//4. Request units/pounds based on product type.
			//5. If valid and quantity is in inventory
				//6. Add to cart, go to step 2.
		//7. else if 0, exit
		//8. else print error, go back to 2.
	//9. Print receipt. If over 50, discount 5%
	updateInventory("items.txt");

	//Delete the inventory. Note the [] required to let delete know we are deleting an array and not a pointer.
	delete [] inventory;
	return 0;
}


bool readInventory(string filename)
{
	//Initialize product array of MAX_INVENTORY size.
	inventory = new Product[MAX_INVENTORY];
	inventoryCount = 0;

	ifstream in(filename);

	if (!in.is_open())
	{
		cout << "Could not open " << filename << endl;
		return false;
	}

	while (!in.eof() && inventoryCount < MAX_INVENTORY)
	{

		Product product;
		in >> product.code;

		if (in.fail())
		{
			cout << "Invalid product code." << endl;
			return false;
		}

		in >> product.name;

		if (in.fail())
		{
			cout << "Invalid product name." << endl;
			return false;
		}

		in >> product.byPounds;

		if (in.fail())
		{
			cout << "Invalid product byPounds (bool)." << endl;
			return false;
		}

		in >> product.cost;

		if (in.fail())
		{
			cout << "Invalid product cost." << endl;
			return false;
		}

		if (product.byPounds)
		{
			in >> product.pounds;

			if (in.fail())
			{
				cout << "Invalid product weight." << endl;
				return false;
			}
		}
		else
		{
			in >> product.units;

			if (in.fail())
			{
				cout << "Invalid product count." << endl;
				return false;
			}
		}

		product.print();

		inventory[inventoryCount] = product;

		inventoryCount++;
	}
	return true;
}

Product * getProduct(int code)
{
	for (int i = 0; i < inventoryCount; i++)
		if (inventory[i].code == code) //If codes match.
			return &inventory[i]; //Returning refrence to inventory[i]
	return NULL;
}

double checkout()
{
	double cost = 0;
	int code;

	while (true)
	{
		cout << "Enter product code: " << endl;
		cin >> code;
		if (cin.fail())
		{
			cout << "Invalid product code!" << endl;
			cin.clear();
			cin.ignore(IGNORE_ARGS);
			continue; //Continue skips all execution in this iteration of the loop, allowing us to jump to the next iteration.
		}

		if (code == 0)
		{
			cout << "Done checking out. Cost: " << cost << endl;
			if (cost > 50)
			{
				cout << "Discount: " << setprecision(2) << fixed << cost * 0.05 << endl;
				cost *= 0.95; //Discount by %5.
			}
			return cost;
		}

		Product * item = getProduct(code);
		if (!item)
		{
			cout << "Item not found.";
			continue;
		}

		if ((item->byPounds && item->pounds <= 0) || (!item->byPounds && item->units <= 0))
		{
			cout << "There's nothing left of that item.";
			continue;
		}


		cout << "Enter " << (item->byPounds ? "pounds" : "weight") << " (max " << (item->byPounds ? item->pounds : item->units) << "): ";

		if (item->byPounds)
		{
			double pounds;
			cin >> pounds;
			if (cin.fail())
			{
				cout << "Invalid weight." << endl;
			}
			else if (pounds > item->pounds)
			{
				cout << "Not enough pounds left of that item." << endl;
			}
			else if (pounds < 0)
			{
				cout << "Can't buy a negative weight (that's called giving)" << endl;
			}
			else
			{
				double added = pounds * item->cost;
				item->pounds -= pounds;
				cout << "Added " << pounds << " pounds of " << item->name << " for $" << setprecision(2) << fixed << added << endl;
				cost += added;
			}
		}
		else
		{
			int units;
			cin >> units;
			if (cin.fail())
			{
				cout << "Invalid weight." << endl;
			}
			else if (units > item->units)
			{
				cout << "Not enough units left of that item." << endl;
			}
			else if (units < 0)
			{
				cout << "Can't buy a negative units (that's called giving)" << endl;
			}
			else
			{
				double added = units * item->cost;
				item->units -= units;
				cout << "Added " << units << " of " << item->name << " for $" << setprecision(2) << fixed << added << endl;
				cost += added;
			}
		}
		//Make sure it's clean for the next iteration.
		cin.clear();
		cin.ignore(IGNORE_ARGS); //So input doesn't keep coming back on fail.
	}

	return cost;
}

bool updateInventory(string filename)
{
	ofstream out(filename);
	for (int i = 0; i < inventoryCount; i++)
	{
		//Write out all elements separated by space.
		out << inventory[i].code		<< " "
			<< inventory[i].name		<< " "
			<< inventory[i].byPounds	<< " "
			<< inventory[i].cost		<< " "
			<< (inventory[i].byPounds ? inventory[i].pounds : inventory[i].units) << endl;
	}
	out.close();
	return false;
}

Removed #define/#ifdef and #include, as they were only used in example.