@Dilshan-Lakshitha Machan first of all this is a community and it's not a place where you get other people to code for free of charge. Even if we wanted to I'm pretty sure most of us don't have enough time but what we can do is help you when you get stuck in some place or you don't know what to do next. Without out giving an effort, there won't be any help.
Ok now let me give you a basic idea how this should be developed.
Get all the Menu Items and prices into a .txt file
eg: - Fried Rice 180
Fried Noodles 200
etc.
Using file reading function read them at the start and get it into a 2D array and print them accordingly.
it should be showed to select. (This may vary according to user's preference)
eg:-
etc.
999.Done
Let the user select using the input method. Make sure the above said is in a loop. I prefer while loop.
Each time the user selects an item add it to an array. I recommend using just numbers as you already have food items on another array.
eg:-
Then at the end of the ordering process when user hits that 999 or Done. Calculate the ordered food array and print it out.
Try this method and see. Else come back to us and someone else or me would be able to help you.