This is an implementation of the Caesar Cipher encryption algorithm written in C. The program takes a single command-line argument, a non-negative integer key, and prompts the user for plaintext. The program then encrypts the plaintext by "rotating" each letter by the key, preserving the case of the letter.
To use the program, compile it with a C compiler and run it with the desired key as a command-line argument. For example:
./caesar 3
This will encrypt the plaintext entered by the user with a key of 3. Negative numbers are also supported, and it will decrypt the text:
./caesar -3
This implementation uses the CS50 library and it's get_string function, as it is an enhancement of a problem set from Harvards CS50. But you can easily replace it by standard C input functions.
As this program is written in C, it is important to be aware of potential security risks such as buffer overflows and other memory-related vulnerabilities. This implementation has been tested and is considered safe for use, but it's always a good practice to be cautious when working with low-level languages like C.