- Write a function that converts Fahrenheit temperatures to
  Celsius.  The definition line should be:

    double fah_to_cel(double temperature)

- Write a function to determine if a number is prime or not.
  The definition line should look like:

    bool is_prime(int n)

- Write a function to duplicate the random number generator
  functionality in Python.  Specifically, make it so you can
  generate a random number with an upper bound and a lower
  bound:

    int gen_random(int lower, int upper)

  This should generate a random number x such that 
  lower <= x <= upper.

- Write functions for the loop problems from the last class.
  Decide on appropriate arguments and return values.