vs2005 C#

How many exceptions should I trap when reading a file ?
                                  let me clarify...

c is my pointer to the processing line

I have this code:
 
       public int ProcessFile(string[] file, int c)
       {
           
           if (c < file.Length && line.IsSegment(file[c]))
           ...

1. if file is null a reference to file c < file.Length will crash.
2. 5 lines on file and c index does not point to the rigth line  (migth be
-10)   crash.    
3. file has 5 lines: when checking file.length c could have -1 (will pass)
but  line.IsSegment(file[c])) will crash, correct?

is it good to use try-catch ?
then, there is no way to know whats going on .
file or index (or what else??)

am i missing any other exceptions?

Thanks