PHP string characterization

Question

I need to specify whether the type of string starts with either 3 digits, 3 letters, or a combination. The string the user types.

The code i have works for letters and numbers, but not for the combinations. What should I do?

 $type = substr($value, 0, 3);
 if(is_numeric($type)){
     echo 'starts with 3 digits';
 }elseif(is_string($type)){
     echo 'starts with 3 alphabetic characters';
 }else{
     echo 'undefined type?';
 }

Answer 1

Your function calls might return unintended results. I recommend ctype_ calls for reliability:

$type = substr($value, 0, 3);
if(ctype_digit($type)){
    echo 'starts with 3 digits';
}elseif(ctype_alpha($type)){
    echo 'starts with 3 alphabetic characters';
}else{
    echo 'undefined type?';
}

p.s. If you want to check if the substring is a combination of letters and numbers, you can can ctype_alnum().