how to get all possible combination (programmatically)

I'm trying to figure out how to write a code that would allow me to get all the possible combination. In this case, I have 4 fruits: apple, orange, grape, mango. I want to know all the possible combination, for example:

apple (a possible combination)
apple,orange (another possible combination)
apple,grape (another possible combination)
apple,orange,grape (another possible combination)
and so on...

I'm assuming order doesn't matter, that is whether (apple, orange), or (orange,apple) they are the same combination.
In which case, the way I would solve it, ironically, is to maintain a strict order, as you have by keeping apple first in your example combinations.
So, treat each fruit like a number from 1 to 4, and generate combinations, where the numbers always have to be in numerical order, and you'll have all your combinations.
1
2
3
4
12
13
14
123
124
1234

See if you can figure a way to loop 4 times when you have 1 item, 3 times when you have 2 items, 2 times when you have 3 items, and 1 time when you have 4 items.

See a pattern?