* Phase 1:  Displays the enter operation prompt in a loop
 *           until 'q' is entered.

   14 lines of code
   while loop
     with one printf and two scanf

 * Phase 2:  Ask for input numbers if operation is a, s, m, or d.

   25 lines of code (11 more)
   switch statement [inside while]
    for a, s, m, or d
     with two printf and two scanf


 * Phase 3:  If operation is d, loop until 2nd number isn't 0

   31 lines of code (6 more)
   if --- test for 'd'
     while -- 2nd number is 0
       printf and scanf

 * Phrase 4:  Perform the operations and print result
   45 lines of code (14 more)
   switch statement
    for a, s, m, or d
     with assignment and printf