Problem Description:

You are a spy! You need software to send secret messages to you partner. Write software that can be used to encrypt and decrypt text messages.

There should be no limit on the size of the message. Your program should first ask the spy if she/he wants to encrypt or decrypt a message. Then, it should ask her/him to enter the message. Your program should print the encrypted or decrypted message based on the user input.

Part 1: Analysis: (5pts)

Describe the problem including input and output in your own words.

Part 2: Design: (5 pts)

(Divide-and-conquer).

Describe the major steps for solving the problem. What methods you used to help you solve the problem.

Use a flow chart to show the design of your system (bonus 3pts).

Part 3: Source code: (20 pts)

Write your code with comments and use descriptive variable names.

Part 4: Testing: (5 pts)

(Describe how you test your program)

Describe what test cases you used to check the validity of your code (you might have more cases). Examples:

1. Entering a message to encrypt

2. Entering a message to decrypt

3. Entering a wrong command (neither encrypts nor decrypt)