The algorithm behind a sudoku solver...?pls help..?

I'm looking to write a program in C or C++ to solve a given sudoku of any difficulty.I understand that a brute force is the method i need to adopt so that i can get the solution for any given grid...but i do not understand how the algorithm works...can someone explain how i need to carry out the iterations so that by trial and error i end up with the solution?Any help will be greatly appreciated..(I'm not asking for the coding itself, just the explanation of the logic..)