noob c++

/g/ doesn't like beginners ;_;

what is the purpose of the for-loop in this program?
i had to make a program to order a couple numbers, and it works, but i'm not sure why the purpose the for-loop has (i know what a for loop is, just not why i need it here)

http://pastebin.com/8Aarr5Ni

I only write code that uses Duff's Device.