Missing Parameters

<?php
function takes_two($a, $b) {
	if (isset($a)) { echo " a is set\n"; }
	if (isset($b)) { echo " b is set\n"; }
}
echo "With two arguments:\n";
takes_two(1, 2);
echo "With one argument:\n";
takes_two(1);
?>

# ผลลัพธ์
With two arguments:
 a is set
 b is set
With one argument:
Warning: Missing argument 2 for takes_two() in .... on line 6
 a is set