how to check for duplicates in random array?

I have an array of 4 numbers and I'm having trouble checking for duplicates. I had the impression that if i randomize numbers for arr[i], then for arr[j], I can compare them for duplicates and randomize again if true. How do I go about checking that element of the array is not repeated/duplicated?

int arr[4];
srand(time(0));

for(int i=0; i<4; i++)
{
    arr[i] = rand() % 10;
    for(int j=i+1; j<4; j++)
    {
        arr[j] = rand() % 10;
        if(arr[j] == arr[i])
        {
            arr[i] = rand() % 10;
        }
    }
}

for(int i=0; i<4; i++)
cout << arr[i] << endl;