Cocoa Objective-C iPhone NSString comparison question?

[jehovaswalrus]

In Objective-C, it is possible to compare two NSString objects by stating:

if ([string1 isEqualToString: string2])
{
//Code
}

How do I compare whether or not string1 is NOT equivalent to string2?
I tried:
if (string1 != string2)
This doesn't work.

 

[Pete S]

Can you not just use the NOT unary operator?

if (![string1 isEqualToString: string2])