How do check an array from repeat numbers in c++?

Im trying to produce an array with 4 random generated [srand seeded rand()] without any repeats. Im using a for loop to:

Select a position in the array, Generate a number, Assign the number to the currently highlighted position Check that the assigned number is not equal to a previous entry

if no -

Then select the next position in the array and generate a new number

if yes -

Do not move to the next array position and generate a new number again.

repeat until array position 3

This was my attempt:

int operator_selection;
int operator_index[3];
int random_value;
for (operator_selection = 0; operator_selection < 4; operator_selection++)
{
    random_value = rand() %4 + 1;

    if (random_value = operator_index[0] || operator_index[1] || operator_index[2])
    {
        (operator_selection - 1);
    }
    operator_index[operator_selection] = random_value;
    cout<<operator_index[operator_selection]<<" ";

    if (operator_selection == 3)
    {
        cout<<endl;
    }
}

However when I run the executable I always end up with repeats, so Im pretty sure the logic behind my first 'if statement' is flawed.

Im a c++ begineer and this is my 3rd attempt at writing a source file from scratch, so appologies if I've made a silly mistake.