在字符串中查找位置X的值

I have a string (product sku): TC00111009 (as example, it can be TTIIIIIII (T=Text,I=Integer))

How I can check that 4th position's TC00[1]11009 value is 1 or 2? Which php functions will fit for this?

You'll be interested in PHP's substr() function:

$value = substr($string, 3, 1);
if (($value == 1) || ($value == 2)) {
    // it's equal to 1 or 2

} else {
    // something else

}

You can also use direct string-index accessing (i.e. treating the string like an array):

$value = $string[3];

If you take this approach, make sure your string is long enough first: if (strlen($string) > 4)

Another way. Positions start with 0 so 3 is the 4th position:

$string = 'TC00111009';

if($string[3] == 1 || $string[3] == 2) {
    //yes
}