Question

I wrote this function to swap values in a multi-dimensional array with my understanding that arrays are pointers.

void
swap(int* a, int* b)
{
    int tmp = *a;
    *a = *b;
    *b = tmp;
}

However when I try to use the function

swap(board[d-1][d-2]), board[d-1][d-33];

I get these errors from the compiler and I don’t know why:

fifteen.c: in function 'init':
fifteen.c:166:9: error: passing argument 1 of 'swap' makes pointer from integer without a cast [-werror]
fifteen.c:45:6: note: expected 'int *' but argument is of type 'int'
fifteen.c:166:9: error: passing argument 2 of 'swap' makes pointer from integer without a cast [-werror]
fifteen.c:45:6: note: expected 'int *' but argument is of type 'int'

How do I fix it?

Answer 1

board[d-1][d-2] and board[d-1][d-33] are int. To swap the both, you have to pass their addresses:

swap (&board[d - 1][d - 2]), &board[d - 1][d - 33];

If you are using swap (board[d - 1][d - 2]), &board[d - 1][d - 33]), the instruction int tmp = *a; will try to access to the value on the address board[d - 1][d - 2]: this make no sense! Because you are using pointers, you have to pass the address of your variables.