how to check if variable is undefined

[Anon]

For example:
I have variable $t,

if $t=1 do something
if $t=2 ...

put if $t is not defined I want it to be 0. I want the variable to be defined in this page, not in the previous. Is it possible?

thanks already...

[[deleted]]

if (isset($var))
{
// $var is defined
}
else
{
// $var is not defined
};