Pointer to 2D array in C

Question

I am trying to make a sudoku solver in C. I have tried to make a function to solve the sudoku and then return the grid.

void solve(int *grid){
    //solve sudoku
}

int main(){
    int[][] grid = {
        {5,3,0,0,7,0,0,0,0},
        {6,0,0,1,9,5,0,0,0},
        {0,9,8,0,0,0,0,6,0},
        {8,0,0,0,6,0,0,0,3},
        {4,0,0,8,0,3,0,0,1},
        {7,0,0,0,2,0,0,0,6},
        {0,6,0,0,0,0,2,8,0},
        {0,0,0,4,1,9,0,0,5},
        {0,0,0,0,8,0,0,7,9}
    };
solve(&grid);
}

This does not seem to work. It needs to take a pointer because it should edit the array not a copy Why is this?

Answer 1

First of all this declaration of an array

int[][] grid = {
    {5,3,0,0,7,0,0,0,0},
    {6,0,0,1,9,5,0,0,0},
    {0,9,8,0,0,0,0,6,0},
    {8,0,0,0,6,0,0,0,3},
    {4,0,0,8,0,3,0,0,1},
    {7,0,0,0,2,0,0,0,6},
    {0,6,0,0,0,0,2,8,0},
    {0,0,0,4,1,9,0,0,5},
    {0,0,0,0,8,0,0,7,9}
};

is wrong. You have to use square brakets after the identifier and specify at least the number of elements in the inner dimension.

#define N 9

//...
int grid[][N]  = {
    {5,3,0,0,7,0,0,0,0},
    {6,0,0,1,9,5,0,0,0},
    {0,9,8,0,0,0,0,6,0},
    {8,0,0,0,6,0,0,0,3},
    {4,0,0,8,0,3,0,0,1},
    {7,0,0,0,2,0,0,0,6},
    {0,6,0,0,0,0,2,8,0},
    {0,0,0,4,1,9,0,0,5},
    {0,0,0,0,8,0,0,7,9}
};

If you want to pass the array to a function then the function can be declared like

void solve( int ( *grid )[N], size_t n );

and called like

solve( grid, N );

Take into account that arrays do not have the copy assignment operator and you may not assign an array identifier with a pointer.