<s>
An	O
undefined	B-Error_Name
variable	I-Error_Name
in	O
the	O
source	O
code	O
of	O
a	O
computer	B-Application
program	I-Application
is	O
a	O
variable	O
that	O
is	O
accessed	O
in	O
the	O
code	O
but	O
has	O
not	O
been	O
declared	O
by	O
that	O
code	O
.	O
</s>
<s>
In	O
some	O
programming	O
languages	O
,	O
an	O
implicit	O
declaration	O
is	O
provided	O
the	O
first	O
time	O
such	O
a	O
variable	O
is	O
encountered	O
at	O
compile	B-Application
time	I-Application
.	O
</s>
<s>
Perl	B-Language
's	O
"	O
use	O
warnings	O
"	O
or	O
Visual	B-Language
Basic	I-Language
's	O
"	O
Option	O
Explicit	O
"	O
)	O
.	O
</s>
<s>
The	O
following	O
provides	O
some	O
examples	O
of	O
how	O
various	O
programming	O
language	O
implementations	O
respond	O
to	O
undefined	B-Error_Name
variables	I-Error_Name
.	O
</s>
<s>
foo.c	O
:	O
In	O
function	O
`main	O
 '	O
:	O
</s>
<s>
foo.c:2	O
:	O
error	O
:	O
for	O
each	O
function	O
it	O
appears	O
in	O
.	O
)	O
</s>
