Generate 8 different Coordination

im trying to write a function that gets an array, generate 8 Different Coordination I have some struct Array size 8 that save some Coordination in other array([8][8]). Im trying to Get eight Different coordination. But Unfortunately, I get some coordination. here is the code :

struct location {
int x;
int y;
};
void setCoordinations(struct locaction loc[]) /// the array is empty.
{
    int i = 0, j = 8; 
    srand(time(NULL));


    array[i]._row = rand() % 8;
    array[i]._coulmn = rand() % 8;
    for (int i = 1; i <8; i++)
    {
        
        array[i]._row = (rand() +i) % 8;
        array[i]._coulmn = (rand() -j)  % 8;
    }

sometimes i get the same coordinations

Thank you for your help.