<?php
error_reporting( E_ALL );
if ( isset( $_POST['submit'] ) )
{//1
$a_data = $a_error = array();

$a_data['v1'] = ( isset( $_POST['v1'] ) ) ? abs( (int)$_POST['v1'] ) : 0 ;
$a_data['v3'] = ( isset( $_POST['v3'] ) ) ? abs( (int)$_POST['v3'] ) : 0 ;
$a_data['v2'] = ( isset( $_POST['v2'] ) ) ? trim( (string)$_POST['v2'] ) : 0 ;

//2
if( strlen( $a_data['v1'] ) > 10 )
$a_error['v1'] = 'zavelike ch1';

$a_v2=array('plus','minus','div','mov');

if (!in_array($a_data['v2'],$a_v2) )
$a_error['v2'] = 'zavelike ch2';

if(strlen($a_data['v3'])>10)
$a_error['v3'] = 'zavelike ch3';
//3
if ($a_data['v2']=='div' and $a_data['v3']==0 )
$a_error['v3'] = 'zavelike ch4';

//4
if ( ! $a_error )
{
switch ( $a_data['v2'] )
{
case 'plus' : echo $a_data['v1'] + $a_data['v3'] ; break;
case 'minus' : echo $a_data['v1'] - $a_data['v3'] ; break;
case 'div' : echo $a_data['v1'] / $a_data['v3'] ; break;
case 'mov' : echo $a_data['v1'] * $a_data['v3'] ; break;
}
}
else
echo 'рпоизлшла ошщибка';
}
?>

<form method="post" action="">
enter v1:
<?php if ( isset( $a_error['v1'] ) )
echo '<span style="color:red;">' . $a_error['v1'] . '</span>'; ?>
<br />
<input name="v1" type="text" size="9" maxlength="10" value="<?php echo @$a_data['v1'] ?>" /><br />

<?php if ( isset( $a_error['v2'] ) )
echo '<span style="color:red;">' . $a_error['v2'] . '</span>'; ?>


<select name="v2">
<option value="plus" <?php if ( @$a_data['v2'] == 'plus' ) echo 'selected="selected"'; ?>>+</option>
<option value="minus" <?php if ( @$a_data['v2'] == 'minus' ) echo 'selected="selected"'; ?>>-</option>
<option value="div" <?php if ( @$a_data['v2'] == 'div' ) echo 'selected="selected"'; ?>>/</option>
<option value="mov" <?php if ( @$a_data['v2'] == 'mov' ) echo 'selected="selected"'; ?>>*</option>
</select><br / >
enter v3:
<?php if ( isset( $a_error['v3'] ) )
echo '<span style="color:red;">' . $a_error['v3'] . '</span>'; ?>
<br />

<input name="v3" type="text" size="9" maxlength="9" value="<?php echo @$a_data['v3'] ?>" />
<input type="submit" name="submit" value="zen" />
</form>