I want to save the indices of my bool vector where the vector element is false.

I have the following code:

```
vector<bool> incumbent_solution; // (0,0,0,1,1,0,0)...
vector<int> I_minus_S(incumbent_solution.size());
auto it = copy_if(incumbent_solution.begin(), incumbent_solution.end(),
I_minus_S.begin(), [&incumbent_solution](auto i) {if (incumbent_solution[i] == 0] return i; });
I_minus_S.erase(it, I_minus_S.end());
```

But it only stores True in my Vector and not the indices. What is my lambda doing wrong?

The `std::copy_if`

works differently than you expected, it passes the actual element to the predicate and copies it into the second container if the predicate returns `true`

.

If you want indexes, use a simple `for`

loop:

```
std::vector<bool> incumbent_solution { 0, 0, 0, 1, 1, 0, 0, 1, 1 };
std::vector<int> I_minus_S(incumbent_solution.size());
std::size_t last = 0;
for(std::size_t index = 0; index < incumbent_solution.size(); ++index) {
if(incumbent_solution[index] == false)
I_minus_S[last++] = index;
}
I_minus_S.erase(I_minus_S.begin() + last, I_minus_S.end());
```