Xcode Cocoa application how can I Nsstring @"", something

So I have a problem... Here is my code.

NSString *targetPath =@"/Users/miguelcosta/Desktop/Image.png";

So in this NSString I want to do something like this...

NSString *targetPath =@"/Users/miguelcosta/Desktop/Image", RandomNumber + @"png";

How can I do that?

I hope that you understand... Thanks for your help!