planning to design an software for an enterprise (stock Maintenance , profit loss calculation , Inventory)

If you planning to develop a windows application then use Visual Studio (C#) but in case of web application for enterprise you can use Visual Studio (ASP.Net,C#) or PHP, MySql.

The logic behind developing a project having Profit and loss calculation, Stock Inventory maintenance, purchase, sales is to go with the development of application in layer wise like Presentation, business and data layer:

Source image MSDN: https://msdn.microsoft.com/en-us/library/ee658109.aspx

Keep these steps in development of ERP type application:

• Design master tables like MasterProduct, MasterCustomer, MasterBuyer etc.
• Design purchase/sale table.
• Design some reports like Purchase/sale calculations.

Actually there are lots of thing that can not understood by writing. I am trying to keep this simple understandable topic.

Now come to the point, First thing first in ERP you have to insert records in master table like if you have some product that you want to sell/purchase then enter it in your database through admin panel. Enter price master details also. When you master tables are ready. You can trade whatever you want.

Simply think, you need to buy a second hand laptop and you have Rs. 20,000 budget in your hand. After buying a second hand laptop you think about re-sale this laptop to someone in Rs. 25,000 and you sell it. Now you have Rs. 5,000 profit in hand.

Now think like a programmer:

1. Create a table [MasterProduct] with "ProductId, ProductName" columns. Enter laptop into this table as product name.
2. Create a table [MasterPrice] with "ProductId, Price" columns. Enter laptop id in this table with price Rs. 20,000.
3. Create a table [Purchase] with "ProductId, Price" columns. Enter laptop id in this table with price Rs. 20,000. (After purchasing laptop)
4. Create a table [Sale] with "ProductId, Price" columns. Enter laptop id in this table with price Rs. 25,000. (After sale to someone)
5. Now you can easily find how much you get as profit or loss.

I have recently developed some ERP type application. You can check live and understand how you can develop this type of applications: 

http://icc.omrtech.com (Username: admin Password: carpet).

That's it. This is a simple solution of a ERP development lifeline. Hope you can understand what I am trying to say. 

Hope this will help you.