<?
# http://..../intro03.php
# http://..../intro03.php?v1=5&v2=10 
# http://..../intro03.php?v1=8
if (empty($v1) or $v1 < 1) { $v1 = 2; }
if (empty($v2) or $v2 < 1) { $v2 = 3; }
if ($v1 == 5) {
  echo "v1 equal five";
} else {
  echo "v1 not equal five";
}
echo "<hr>";  # =====
if ($v1 == 8) {
  echo "v1 equal eight";
} else {
  if ($v1 == 2) {
    echo "v1 equal two";
  } else {
    echo "v1 not equal eight and two";
  }
}
echo "<hr>";  # =====
if ($v2 == 3) { echo "v2 equal three"; }
elseif ($v2 == 10) { echo "v2 equal ten"; }
elseif ($v2 == 6) { echo "v2 equal six"; }
else { echo "v2 not equal three and ten and six"; }
?>