filling a matrix in C

[Force Flow]

I'm having a problem trying to fill a 6x6 matrix in C

Filling it like this is a piece of cake:

 0   1   1   1   1   1
-1   0   1   1   1   1
-1  -1   0   1   1   1
-1  -1  -1   0   1   1
-1  -1  -1  -1   0   1
-1  -1  -1  -1  -1   0

But I'm having a real hard time trying to fill it like this without having to define almost every single cell:

1   1   1   1   1   0
1   1   1   1   0  -1
1   1   1   0  -1  -1
1   1   0  -1  -1  -1
1   0  -1  -1  -1  -1
0  -1  -1  -1  -1  -1

Is there a way to invert the matrix from the "piece of cake" one?

Here's what I have so far, such as it is.

[Force Flow]

Updated:

I got the diagonal line. Now I just need to figure out how to fill 2 sides. I'm puzzled in this respect.

[Paul Victorey]

Well, let's look at a for loop:

for (int i = 0; i < rows; i++){
  for (int j = 0; j < cols; j++){
  }
}

and let's put the values of i and j by the array:

 | 0   1   2   3   4   5  = j
   -   -   -   -   -   -
0| 1   1   1   1   1   0
1| 1   1   1   1   0  -1
2| 1   1   1   0  -1  -1
3| 1   1   0  -1  -1  -1
4| 1   0  -1  -1  -1  -1
5| 0  -1  -1  -1  -1  -1
=
i

Now, what condition do we have a 1? If (5-j) > i
We have a 0 when (5 - j) == i
And a -1 when (5 - j) < i

[Force Flow]

Great! It worked! Thanks a million, Paul Victorey It was driving me up the wall