reading text from a file into your program

Let me explain before I ask my question.

You have a program that simply reads a string into a variable, from a text file. Now, there was a program that did this for me, from a tutorial.

The weird thing was this. I tried messing around with it to see if I could make it mess up. I typed in NULL for the string in the text file, and it woudn't read in the string correctly! I thought it would read in, literally, "NULL", but putting that in made it mess up!

1) What are some other keywords or special things that could make it mess up?

2) Why would that have made it mess up, and not take in the string "NULL"?

Thats odd. It shouldn't care what the text string is.

How is it messing up? Can you post the code?