checking if a string is with in a different string

FROM : Tom Hancocks
DATE : Wed Apr 13 15:22:59 2005

Sorry thats worded badly but i couldn't think of how else to put it,
anyways. I have recently moved from RB, as stated in previous posts of
mine, and i'm still trying to get to grips with it all, but i must say
i am getting there, thankfully.

I'm creating a search function for my program, and in RB i would of
used the InStr function to check if a string occured in side another
string for example

searchString        :World
string            :Hello World
Found            :YES

like i said i would of done

if instr(String,SearchString)>0 Then
   //It was found
else
   //not found
end if

In Obj-C i have tried to do this:

if ([string compare:searchString] == NSNotFound){
   //Not Found
}else{
   //Found
}

but it has not worked, could anyone help me out and tell where i'm
going wrong?