A sudoku solver made in C as a little summer project.

Puzzle is inputted as numbers in a txt file (puzzle.txt), here are some to test it out on:

medium
0 2 7 3 0 6 0 0 9
6 0 9 7 0 2 8 0 1
5 0 0 0 8 0 0 7 0
0 0 0 0 7 0 4 1 0
0 8 5 9 0 0 7 0 3
0 7 0 1 6 0 0 0 8
7 0 3 0 0 0 0 8 0
0 0 8 0 0 7 0 0 0
4 9 6 2 0 8 1 5 0

hard
0 0 0 0 5 0 6 0 3
0 0 3 6 0 0 9 0 0
8 0 0 0 1 0 4 2 0
0 2 9 0 0 5 8 0 0
0 5 0 0 2 0 0 4 9
0 7 0 0 0 1 2 5 0
0 0 0 4 0 0 0 0 2
4 0 7 0 0 0 5 0 0
0 1 0 0 0 0 7 0 0

expert
2 0 0 0 7 9 1 0 0
0 3 7 5 0 2 0 8 0
0 0 0 0 4 0 0 2 0
0 2 0 0 0 0 0 0 0
0 1 0 0 0 0 2 0 8
9 7 6 1 2 8 0 0 0
7 6 0 0 3 4 0 0 0
1 0 3 0 0 0 0 7 0
0 0 0 7 6 0 9 3 0