- Write a function that simulates the behaviour of the atoi function in Go. Atoi transforms a number defined as a `string` in a number defined as an `int`.
- Atoi returns `0` if the `string` is not considered as a valid number. For this exercise **only valid**`string` chains will be tested. They will only contain one or several digits as characters.
- For this exercise the handling of the signs + or - does not have to be taken into account.
- This function will **only** have to return the `int``nbr`. For this exercise the `error` return of atoi is not required.