What's better/faster? Try-catch or avoid exception?

Question

I would like to know, what's better or/and faster in general programming? Avoid the exception or wait for the exception?

Avoid the exception would be:

string a = null;
list = someMethod();
if(list.Length > 0 ){
   a = list[0];
}
if(a!=null) ...

Or try catch exception...

string a = null;
try{
    a = someMethod()[0];
catch{}
if(a!=null) ...

Answer 1

Performance is not the most relevant concern here. The question is, which of the two leads to more readable/maintainable/testable programs. You can worry about performance later.

In general, don't use exceptions for flow control. They are effectively a non-local goto which makes programs more difficult to read and follow. As such, they should be reserved for exceptional situations. If you can get away with not using a try-catch block for flow control, don't. Your programs will be more readable and maintainable.

The "right" way to handle this situation is

var list = someMethod();
if(list == null || list.Length == 0) {
    // handle something bad
}
string a = list[0];
if(a != null) {
    // go
}

You can avoid the check that list is not null and not empty if there is a contract (Contract.Ensures) that guarantees the return value from someMethod is not null and not empty.

It is true, however, that exceptions are locally expensive. Whether or not they will impact the performance of your program (i.e., are a bottleneck) is another question altogether. But used properly, exceptions are generally not a bottleneck (who cares about performance when your application is crashing?)