Darkstar | A Xerox Star 8010 Emulator | Machine Learning library

When I run my code it throws a segmentation fault and I have tried rewriting the code several times. Still to no avail, it won't even run. The segmentation fault happens as soon as my program is launched. What it's supposed to do is print a path on screen using the ncurses library in Linux, from the given coordinates. Here is the problematic snippet with the lines where gdb said the segmentation fault was, also it (snippet) reproduces the problem.

EDIT: This will help explain what I'm trying to do, but using dynamic arrays. Breadth First Search

EDIT 2: The variable frontier is supposed to keep track of the X and Y values at a specific index. The add_neighbors function is there to add all four neighbors (providing they aren't already added) to the frontier and came_from arrays.

frontier[index][0] is X value.
frontier[index][1] is Y value.

The before the first while loop I set the start position x1 and y1. During the first while loop, it increments getting the new coordinates from the frontier, then processing and adding to came_from array.

For example:
(x1,y1) (x1+1,y1)
(x1,y1+1) (x1+1,y1+1)
(x1,y2) (x2,y2)

I'm trying to get from (x1,y1) to (x2,y2). Sure hope that explains it better. What I'm trying to implement is a Breadth First Search (BFS) algorithm. Using two arrays, one is frontier (keeps track of visited positions) and came_from (keeps track of X and Y the path from x1,y1 to x2,y2). Updated the code to reflect the first answer. Plus added a comment to explain where the error might be, not really sure but I've been debugging it. It looks like the came_from array never gets set with x and y.

The Code: