The root cause of this error is that the value of `x` is being
initialized to 1.0 and then multiplied by 0.0 in the first iteration
of the for loop in the `fact` function. This causes `x` to be 0.0,
which triggers the assertion failure in the `fact` function. The
subsequent multiplications in the following iterations of the for loop
also result in `x` being 0.0, which is then returned and printed in
the `main` function.

To fix this, we need to initialize `x` to 1.0 and start multiplying
from 1.0 instead of 0.0. The corrected code for the `fact` function
is:

```
float fact(float n) {
  auto x = 1.0;
  for (auto i = 1.0; i <= n; i++) {
    x *= i;
  }
  assert(x != 0.0);
  return x;
}
```