There are a lot of ways you can do encryption, Just decide which way you want to proceed.. Which mode of operation you want to do. Which sequence you want to follow when you are XOR ing the data. Do...

Couple of suggestions,
1. Avoid using global variables as you used choice here..
2. you can further shrink the main by moving choices to methods here..
3. Display result can also be another...

I really didnt understand your question, as per my understanding..