Write a function isOldEnough that takes an input called num as an argument. The function should return either true or false based on the following logic:
- It returns true if the number is greater than or equal to 18
- It returns false if the number is non-negative but less than 18
- It returns "Invalid argument" if the number is negative or if it's not a number at all
What have you done so far? What seems to be the problem? What language are you working in?
Have a look at https://www.tutorialspoint.com/cplusplus/cpp_if_else_statement.htm for an overview of if-else statements and then come back with more questions.