variable definition error not caught when using strict and warnings

[Nemana, Satya]

Hi

I am a little confused with this program

Program:
use strict;
use warnings;

if ($999 == 1056)
{
    print ("\nequal");
}
else
{
    print ("\nnot equal");
}

What I expect: Perl to throw me an error as $999 variable is not defined, but 
perl executes the code with a warning.(I don't expect the code to compile at 
all)

Output:
Use of uninitialized value in numeric eq (==) at wrong1.pl line 4.

not equal


However, if I replace $999 with $num (which is not defined or initialized), I 
get the following error

Global symbol "$num" requires explicit package name at wrong1.pl line 4.
Execution of wrong1.pl aborted due to compilation errors.

What is happening with the top program?

Thanks in advance
sn