how to make a function which takes as many argument as need by user

I have a project about cafeteria management in which you can online buy something and i do this project in c++......

but when i make my project the problem arrives that if someone order two things and so two arguments added but if other one order 25 things so 25 arguments added so how function knows that how many arguments gone for adding.....

so please can you tell me what can i do that my function knows that how many arguments gone for adding ............

or if i made a new function for adding....

i googled mu query and never received valid answer......

please help me........