Exercise 8.11 (Telephone Number Word Generator)

Standard telephone keypads contain the digits 0 through 9. The numbers 2 through 9 each have three letters associated with them, as is indicated by the following table:

Digit	Letter
2	abc
3	def
4	ghi
5	jkl
6	mno
7	prs
8	tuv
9	wxy

Many people find it difficult to memorize phone numbers, so they use the correspondence between digits and letters to develop seven-letter words that correspond to their phone numbers. For example, a person whose telephone number is 686-2377 might use the correspondence indicated in the above table to develop the seven-letter word "NUMBERS"

Businesses frequently attempt to get telephone numbers that are easy for their clients to remember. If a business can advertise a simple word for its customers to dial, then no doubt the business will receive a few more calls.

Each seven-letter word corresponds to exactly one seven-digit telephone number. The restaurant wishing to increase its take-home business would surely do so with the number 825-3688 (i.e. "TAKEOUT").

Each seven digit phone number corresponds to many separate seven-letter words. Unfortunately, most of these represent unrecognizable juxtapositions of letters. It's possible, however, that the owner of a barber shop would be pleased to know that the shop's telephone number 424-7288, corresponds to "HAIRCUT". A veterinarian with a phone number 738-2273 would be pleased to know that the number corresponds to "PETCARE".

Write a C++ program that, given seven-digit number, writes to a sequenctial file every possible seven-letter word corresponding to that number. There are 2187 (3 to the 7th power) such words. Avoid phone numbers with the digits 0 and 1.