#include <iostream.h>
#include <fstream.h>
;
//define structure
struct item
{
	short code;
	short onHand;
};
const arraySize = 10;
item items[arraySize];
//function prototype
void getData(item []);
void recordPurchase();
void recordSales();
void updateFile();
void record(short, short);
void main()
{
	short choice;
	
	getData(items);
	//display menu
	do
	{
	cout << "Make a choice "<<endl<<endl;
	cout<< "1. To Record a Purchase\n";
	cout <<"2. To Record a Sale\n";
	cout <<"3. To Update Inventory File\n";
	cout <<"4. Quit\n";
	cin >> choice;
	switch (choice)
	{
	case 1:recordPurchase();
		break;
	case 2:recordSales();
		break;
	case 3:updateFile();
		break;
	case 4:cout<< "Thanks and bye\n";
		break;
	default:cout << "Enter a number from 1 to 4 inclusive\n";
	}
	}
	while (choice !=4);
}
void getData(item items[])
{
	short i = 0;
	ifstream infile;
	infile.open("invent.txt", ios::in|ios::nocreate);
	if (!infile.fail())
	{
		infile>>items[i].code>>items[i].onHand;
		while (!infile.eof())
		{
			i++;
			infile>>items[i].code>>items[i].onHand;	
		}
		infile.close();
	}
	else
		cout << "\nError in opening file\n";
	for (i = 0; i<10;i++)
		cout << items[i].code <<" " <<items[i].onHand<<endl;
}
void recordPurchase()
{
	short ic, purch;
	cout<<"\nEnter item code and amount of purchase ";
	cin >> ic >> purch;
	record(ic, purch);
	for (short i = 0; i<10;i++)
		cout << items[i].code <<" " <<items[i].onHand<<endl;
}
void recordSales()
{
	short ic, sales;
	cout<<"\nEnter item code and amount of sales ";
	cin >> ic >> sales;
	record(ic, -sales);
	for (short i = 0; i<10;i++)
		cout << items[i].code <<" " <<items[i].onHand<<endl;
}
void updateFile()
{
	ofstream outfile;
	outfile.open("invent.txt", ios::out);
	for (short i=0; i<arraySize; i++)
		outfile << items[i].code << " "<<items[i].onHand<<endl;
	outfile.close();
	cout<<"\nFile has been updated\n";
}
void record(short ic, short ps)
{
	for (short i = 0; i< arraySize; i++)
		if (items[i].code == ic)
			items[i].onHand += ps;
}