It was a night like any other: I was procrastinating on my programming homework by working on another project when my flatmate came over.
“Hey Matt,” he said, “you’re good with C. I’m having some trouble printing a string.”
“Okay, what’s the problem?”
“So the string is a domain name, but instead of dots, it has a number telling
you how many characters are in the next chunk of the name. So like
3www6google3com. So my question is, how do I convert a character into a number?”
“Ah, that’s easy,” I said, “just subtract a
“What?” he asked. He’s not a C programmer, and so didn’t know this simple trick.
“ASCII has the digit characters arranged sequentially, so the
'3' character is
three larger than the
'0' character. So if you subtract a
'0' from a
you just get
Through some more explanation and description by my flatmate, I figure out that
it’s not actually a
'3' character, but a character with the value
'0' subtraction required!
“Okay, so you get the first character, spit out that many characters, you know the next one is a number, so you repeat that until you hit the end of the string. What’s the problem?”
“Well,” he said, “I’m trying to print out
test.domain.com but it’s not printing
“Ah ha!” I said. “You’re probably trying to print a character that messes with your text. Like, there’s a backspace ASCII character that deletes the last character printed.”
“It goes back to when we had teletypes instead of terminals. Not important right
now. So, your last character before
domain gets deleted.
domain is 6
characters, so I bet the backspace character has value 6.”
I look up an ASCII table. “Aw darn, the backspace character is value 8, not 6. Must be some other problem. Let me take a look at your code.”
“Oh wait,” he said. “It’s not
mydomain. 8 characters. So the prefixed
8 was causing the last
to get deleted. Another mystery solved. I went back to my project and my
flatmate went back to his.
Tune in next time for more…