[ios] NSDictionary - Need to check whether dictionary contains key-value pair or not

I just need to ask something as follow. Suppose I am having a dictionary.

NSMutableDictionary *xyz=[[NSMutableDictionary alloc] init];
[xyz setValue:@"sagar" forKey:@"s"];
[xyz setValue:@"amit" forKey:@"a"];
[xyz setValue:@"nirav" forKey:@"n"];
[xyz setValue:@"abhishek" forKey:@"a"];
[xyz setValue:@"xrox" forKey:@"x"];

Now, I need to check as follows

[xyz does contains key "b" value ?? pair or not?

Question is How?

The other question is How to just count total key-value pair?

Say for example NSInteger mCount=[xyz keyCounts];

With literal syntax you can check as follows

static const NSString* kKeyToCheck = @"yourKey"
if (xyz[kKeyToCheck])
  NSLog(@"Key: %@, has Value: %@", kKeyToCheck, xyz[kKeyToCheck]);
else
 NSLog(@"Key pair do not exits for key: %@", kKeyToCheck);