How does one find a '.' in a string object in Object-C

I am working on getting a simple calculator working as part of my adventure to learning Object-C and iOS development.

In Object-C using NSString, how does one look for a period in a string?

Based开发者_StackOverflow on the comments this is what I got so far.

NSString * tmp = [display text];

NSLog(@"%@", tmp); // Shows the number on the display correctly

int x = [tmp rangeOfString:@"."].location;

NSLog(@"%i", x); // Shows some random signed number 

if (x < 0) {
    [display setText:[[display text] stringByAppendingFormat:@"."]]; 
} 

It is still not working :(

NSRange is a straight-up struct...

typedef struct _NSRange {
      NSUInteger location;
      NSUInteger length;
} NSRange;

int x = [@"hello.there.ok" rangeOfString:@"."].location;
printf("x is %d\n",x);

prints 5.

and here is a whole program:

int main(int argc, char *argv[])
{
    NSString *ht = @"This is a string";
    int r1 = [ht rangeOfString:@"is"].location;
    int r2 = [ht rangeOfString:@"is a"].location;
    int r3 = [ht rangeOfString:@"isnt"].location;
    NSLog(@"r1=%d, r2=%d, r3=%d, that's all\n",r1,r2,r3);
}

which prints:

Program loaded.
run
[Switching to process 21098]
Running…
2011-01-14 20:45:25.192 DELETEME[21098:a0b] r1=2, r2=5, r3=-1, that's all

running this in XCode, Mac OS... should be straightahead!