cant find the problem with this function/loop

[jopeters]

I have two functions here. One of them, get_spectro(), generates a random number between 12-37 to represent a fake number of elements. display_spectro() uses the number generated by get_spectro() to find the number of each of the different elements found. For example, if get_spectro() randomly generates a 12, that means that 12 difference elements were found. display_spectro() then generates a random number 12 times to simulate the 12 difference elements. The problem is I need the 12 elements to be different.

I cant seem to figure out why my code below is not giving me mutually exclusive elements. I thought the combo of a for and while loop I have under display_spectro() would ensure that there were no repeats, but after running it a couple times I still get the same number twice once in a while.

int rover::get_spectro()
//Simulates finding between 12-37 different elements in the core samples
{
	srand(time(0));
	
	int num_elements;
	num_elements = 12 + rand() % 25;

	return num_elements;
}

void rover::display_spectro()
//Generates a random number for each element type in the core sample
//between 1-109.  This number represents one of the first 109 elements
{
	vector<int> element;

	int num_elements = rover::get_spectro();
	int elem_num;

	for(int count =0; count < num_elements; count++)
	{
		elem_num = 1 + rand() % 109;
		element.push_back(elem_num);

		for(int num =0; num < element.size()-1; num++)
		{
			while(elem_num == element[num])
			{
				elem_num = 1 + rand() % 109;
                                element.pop_back();
                                element.push_back(elem_num);
			}
		}
	}

	cout << endl;
	for(int count =0; count<element.size(); count++)
		cout << element[count] << endl;
}

[jopeters]

Well I was going to post an example of the output numbers but now I cant get it to fail...If I get any repeats I will post.

[quirkyusername]

pop_back() just removes the last element that was added to the vector, you want to erase the element at num.

replace element.pop_back(); with element.erase(element.begin() + num);

[jopeters]

But the last element is what I am making sure isnt a copy. If the last element is a copy of another element then I pop_back() to remove it and then push_back() a replacement, doesn't that make sense?