When should I use nil and NULL in Objective-C?

There is a difference in some contexts.

Literally, Null is a character: ASCII 0.

Nil is equivalent to blank, no value.

Depending on the programming context, this can be a big difference.

Beware that `if([NSNull null])` returns `true`.

You can use `nil` about anywhere you can use `null`. The main difference is that you can send messages to `nil`, so you can use it in some places where `null` cant work.

In general, just use `nil`.

nil means absence of value while NULL represent No Object,

NSArray *array = @[@"Hello World !", @101,[NSNULL null] ];

Here [NSNULL null] is an object which means no object, at the same time you cannot add nil to indicate absence of object.

you can use both nil and [NSNUll null] for checking too.

This will help you to understand the difference between nil, NIL and null.

The below link may help you in some way:

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> nil -> literal null value for Objective-C objects.
>
> Nil -> literal null value for Objective-C classes.
>
> NULL -> literal null value for C pointers.
>
> NSNULL -> singleton object used to represent null.

Basically:
nil: null pointer on an object and
null: is for other type pointer

**nil** is an object pointer to nothing.
Although semantically distinct from **NULL**, they are technically **equivalent** to one another.

On the framework level, Foundation defines **NSNull**, which defines a class method, +null, which returns the singleton NSNull object. **NSNull** is different from **nil** or **NULL**, in that it is an **actual** **object**, rather than a zero value.

Additionally, in Foundation/NSObjCRuntime.h, **Nil** is defined as a **class** **pointer** to nothing.

[Refer this for further info - nil / Nil / NULL / NSNull][1]


[1]:

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"nil / Nil / NULL / NSNull"