An array of structures in C...

Answer 1

This creates and initializes a two-dimensional array of structures, with each row containing three. Note that you haven't provided an initializer for the array[1][2], which in this case means its contents is undefined.

struct foo {
    const char *x;
    int y;
};

int main()
{
    struct foo array[][3] = {
        {
            { "foo", 2 },
            { "bar", 5 },
            { "baz", -1 },
        },
        {
            { "moo", 44 },
            { "goo", 200 },
        }
    };
    return 0;
}

EDIT: Made x pointer to const string. Try to make your examples close to your real code.

Answer 2

I think the easiest approach would be to split up the struct and array declarations:

struct foo {
    int x;
    int y;
};

int main()
{
    struct foo foo_inst = {1, 2};
    struct foo foo_array[] = {
        {5, 6},
        {7, 11}
    };
    struct foo foo_matrix[][3] = {
        {{5,6}, {7,11}},
        {{1,2}, {3,4}, {5,6}}
    };

    return 0;
}

The problem is that nested array declarations in C (and C++) cannot have arbitrary length for any array except the outermost. In other words, you can't say int[][] arr, and you must instead say int[][5] arr. Similarly, you can't say int[][6][] arr or int [][][7] arr, you would have to say int[][6][7] arr.