PHP

Validating Form Input: Drop-Down Menus

You want to make sure that a valid choice was selected from a drop-dowm menu generated by the HTML select element.

Use in_array(). You create an array of values to generate the menu. Then validate the input by checking that the value is in the array.

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
"DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="EN" lang="EN">
<head>
<title>PHP</title>
<meta Name="Author" Content="Hann So">
</head>
<body>
<p>
<?php
$fruits = array('Apples', 'Grapes', 'Bananas');

// use $_SERVER[PHP_SELF] is the same as $_SERVER[SCRIPT_NAME]

function display_form($array) {
echo <<<HTML
<form action = "$_SERVER[PHP_SELF]" method="post">
HTML;
echo "<select name='fruit'><br />";
echo "<option></option><br />";
foreach ($array as $choice) {
	echo "<option>$choice</option><br />";
}
echo <<<EOF
</select>
<input type="submit" value="Submit" />
</form>
EOF;
}

// validating the menu
if (in_array($_POST['fruit'], $fruits)) {
	echo 'Your selection is '.$_POST['fruit'];
}
else {
	echo "Select a valid choice.";
	display_form($fruits);
}
?>
</p>
</body>
</html>

View the effect

Use array_key_exists() to validate.

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
"DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="EN" lang="EN">
<head>
<title>PHP</title>
<meta Name="Author" Content="Hann So">
</head>
<body>
<p>
<?php
$fruits = array('red'=>'Apples', 'green'=>'Grapes', 'yellow'=>'Bananas');

function display_form($array) {
echo <<<HTML
<form action = "$_SERVER[PHP_SELF]" method="post">
HTML;
echo "<select name='fruit'><br />";
echo "<option value=''></option><br />";
foreach ($array as $key =>$choice) {
	echo "<option value='$key'>$choice</option><br />";
}
echo <<<EOF
</select>
<input type="submit" value="Submit" />
</form>
EOF;
}

// validating the menu
if (array_key_exists($_POST['fruit'], $fruits)) {
	echo 'Your selection is '.$_POST['fruit'];
}
else {
	echo "Select a valid choice.";
	display_form($fruits);
}
?>
</p>
</body>
</html>

View the effect