a$)$ Write a recursive function in $C++$ with the following prototype:

int getWholeNumber$($string s$)$;

The function should recognize a possibly empty sequence of base $10$ digits and return the corresponding value as a nonnegative integer, or return $-1$ if the string contains any non$-$digits. For the recursive case, call the function on s$.$substr$(0,$ s$.$length$-1).$ In the special case where $s$ is empty string, the function should return $0.($This can be your base case.$)$

b$)$ Write a function int getInteger$($string s$,$ bool & isValid$)$; that recognizes valid integers. That means a nonempty sequence of digits, possibly preceded by a single minus sign. If the string is not a valid integer, then the function should set isValid to false and return $0.$ If the string is a valid integer then the function will set isValue to true and return the corresponding integer value. Your code should call getWholeNumber from Part $a.$