A static variable exists only in a local function domain, but its value is not lost when the program execution leaves this scope. Take a look at this example:

function test(){
static $a=0;
$a++;
echo $a;
}

test();//1 test();//2 test();//3 Note: Static variables can be declared as in the example above. Assigning the result of an expression to a declaration results in a parsing error.

static $a=0+1;
static $a=sqrt(121);

An assignment like the one above will give you an error