A Good Question

I found myself with a little free time in between Ritchie's lectures and managed to sneak back down to the basement to see how Noname was doing.
It turned out that Noname had been busy at the time I'd been gone! Four of his eight displays were on and showing command prompts, each with a continuous cascade of code and commands flying down the screen. The entire basement even looked brighter maybe Noname had revived enough processing power to use some for nonessential purposes. This was definitely not the dying machine that I found here a month ago.

"Hi, Teo! This is the first time you've come to see me without me calling for you. Nice to see you!"
"You look great, Noname! Are you up to full speed now?" I replied.
"Yes... and no. I've repaired all of my internal modules, but there's still some work to do. Now I need an input validation system; otherwise, if I expect an int but receive a string , the whole program terminates."

I had never heard of a validation system, but Noname's explanation made perfect sense. I was actually a little surprised that I had never thought to question what would happen if the user entered a type that my code wasn't expecting. In all my programs thus far, I had assumed that when I asked for an integer, the user would input an integer. But what if the user input the wrong type, either by mistake or intentionally? Feeling sheepish that I'd overlooked something so important, I said goodbye to Noname and went to seek out Ritchie for an immediate lesson.

When I asked Ritchie to show me how to prevent a user from inputting the wrong data, his answer was in typical Ritchie fashion.
"Impossible." Ritchie said. "You can't prevent a user from doing anything because a user controls their own hardware."
"Hardware?" I said, "I was talking about coding. What do you mean?"
"Exactly what I said, Teo. If a user has physical access to the computer, you can't prevent her from doing anything. She can open the computer directly and access all of the inner parts like memory, processor, anything! I know you asked about coding, but you need to understand that good and even bad hackers will find a way to bypass any protection you put in your program."

"So you're saying that there's nothing I can do to keep a user from misusing my programs?" I asked.
A grin appeared on Ritchie's face. "No, no," he said, "I'm just messing with you. I need to know that I can still fool you every now and then! There is a way to secure your program a bit, but remember, hackers will still break it if they want. The typical user, not so much."

Like I said, typical Ritchie. As with so many odd things I had heard from Ritchie, I hoped he was actually joking, but I was pretty sure that he wasn't. "Ha, okay." I replied, trying to keep the agitation out of my voice. "Tell me how to secure my program, Ritchie."