check if a string is valid in php using regex code example

Example: regex validation of name in php

case 3:
                $rgx = "/^[A-Z0-9._%+-]+@[A-Z0-9.-]+.[A-Z]{2,4}$/i";
        break;

        case 2:
                //read below
                $rgx = "/[^A-Za-z0-9]+/";
        break;

        case 1:
                //read below
                $rgx = "/[^A-Za-z0-9]+/";
        break;

        case 0:
                //if characters are NOT normal
                $rgx = "/[^A-Za-z0-9]+/";
        break;

        default:
                echo "???";
                die("$unit ?");
        break;
}

$n = preg_match($rgx, $unit, $matches);
if ( ($idx == 0) || ($idx == 1) || ($idx == 2) ){
        if ($n) {
                echo "Bad Characters in $unit; Alphanumeric only";
        }
} else {
        if ($n == 0) {
                echo "Incorrect Format in $unit; Enter Valid Info";
        }
}