Undefined Offset 1 and 2 - php

Question

I am having Undefined 1 and 2 on line 32 and 33. I don't even have an idea of what is going on and what the error means. How can i fix this please?
$splittedGSM = str_split($gsm);
$correctGSM = TRUE;
if(count($splittedGSM ) != 11) $correctGSM = FALSE;
if($splittedGSM[0] != 0) $correctGSM = FALSE;
if($splittedGSM[1] != 7 && $splittedGSM[1] != 8 && $splittedGSM[1] != 9) $correctGSM = FALSE; //Line 32
if($splittedGSM[2] != 0 && $splittedGSM[2] != 1) $correctGSM = FALSE; //Line 33
foreach ($splittedGSM as $realgsm) {
if(!is_numeric($realgsm)){
return FALSE;
}
}

Answer 1

Try Below code. Offset is not defined because it's not set you have to check that if it's not set then offset will be null. You have to use isset() function for it.
$splittedGSM = str_split($gsm);
$correctGSM = TRUE;
// check using isset function
if(!isset($splittedGSM[1]))
{
$splittedGSM[1] = null;
}
if(!isset($splittedGSM[2]))
{
$splittedGSM[2] = null;
}
if(count($splittedGSM ) != 11) $correctGSM = FALSE;
if($splittedGSM[0] != 0) $correctGSM = FALSE;
if($splittedGSM[1] != 7 && $splittedGSM[1] != 8 && $splittedGSM[1] != 9) $correctGSM = FALSE; //Line 32
if($splittedGSM[2] != 0 && $splittedGSM[2] != 1) $correctGSM = FALSE; //Line 33
foreach ($splittedGSM as $realgsm) {
if(!is_numeric($realgsm)){
return FALSE;
}
}

Answer 2

The problem is that you try to access elements 1 and 2 of $splittedGSM without first checking that they exist. You are probably calling str_split with an empty string as argument, in which case a one-element array containing the empty string will be returned. This explains why you don't get an error when accessing $splittedGSM[0].
As you require a valid result to contain 11 elements, you can solve the problem by only accessing the array elements if the length test is satisfied, using elseif instead of if:
$splittedGSM = str_split($gsm);
$correctGSM = TRUE;
if(!is_array($splittedGSM) || count($splittedGSM ) != 11){
$correctGSM = FALSE;
}elseif($splittedGSM[0] != 0){
$correctGSM = FALSE;
}elseif($splittedGSM[1] != 7 && $splittedGSM[1] != 8 && $splittedGSM[1] != 9){
$correctGSM = FALSE;
}elseif($splittedGSM[2] != 0 && $splittedGSM[2] != 1){
$correctGSM = FALSE;
}
foreach ($splittedGSM as $realgsm) {
if(!is_numeric($realgsm)){
return FALSE;
}
}