- Write a function that transforms a number within a `string`, in an `int`.
- For this exercise the handling of the sign `-`**has** to be taken into account. If the sign is encountered before any number it should determine the sign of the returned `int`.
- For this exercise the handling of the `-` sign**has** to be taken into account. If the sign is encountered before any number it should determine the sign of the returned `int`.
- This function will **only** return an `int`. In case of invalid input, the function should return `0`.