Matrices

Multi-dimensional structures of elements of the same type
Fixed-sized implemented as multi-dimensional arrays
typedef double Transform3D[4][4];

IdentMat(Transform3D m)
{
    register int i;
    register int j;

    for (i = 3; i >= 0; --i)
    {
        for (j = 3; j >= 0; --j)
            m[i][j] = 0.0;
        m[i][i] = 1.0;
    }
}
Variable-sized matrices are handled through pointers to elements, but accessed using the array syntax:
        double **mat = (double **)xmalloc(rows * sizeof(double *));
        for (i = 0; i < rows; i++)
                mat[i] = (double *)xmalloc(cols * sizeof(double));
N dimensions can also be mapped into a flat structure using multiplication.