One technique that can be used to help break some simple forms of encryption is frequency analysis. This analysis examines the encrypted text to determine which characters are most common. Then it...

One technique that can be used to help break some simple forms of encryption is frequency analysis. This analysis examines the encrypted text to determine which characters are most common. Then it tries to map the most common letters in English, such as E and T, to the most commonly occurring characters in the encrypted text.

Write a program that initiates this process by determining and displaying the frequencies of all of the letters in a file. Ignore spaces, punctuation marks, and digits as you perform this analysis. Your program should be case insensitive, treating a and A as equivalent. The user will provide the name of the file to analyze as a command line argument. Your program should display a meaningful error message if the user provides the wrong number of command line arguments, or if the program is unable to open the file indicated by the user.