[php] How to fix Warning Illegal string offset in PHP

I have this chunk of PHP code which is giving me the error:

Warning: Illegal string offset 'iso_format_recent_works' in C:\xampp\htdocs\Manta\wp-content\themes\manta\functions.php on line 1328

This is the code that the warning is relating to:

if(1 == $manta_option['iso_format_recent_works']){
    $theme_img = 'recent_works_thumbnail';
} else {
    $theme_img = 'recent_works_iso_thumbnail';
}

When I do an a var_dump($manta_option); I receive the follow result:

["iso_format_recent_works"]=> string(1) "1"

I have tried casting $manta_option['iso_format_recent_works'] to an int but still get the same issue.

Any help would be greatly appreciated!

Please check that your key exists in the array or not, instead of simply trying to access it.

Replace:

$myVar = $someArray['someKey']

With something like:

if (isset($someArray['someKey'])) {
    $myVar = $someArray['someKey']
}

or something like:

if(is_array($someArray['someKey'])) {
    $theme_img = 'recent_works_iso_thumbnail';
}else {
    $theme_img = 'recent_works_iso_thumbnail';
}

1.

 if(1 == @$manta_option['iso_format_recent_works']){
      $theme_img = 'recent_works_thumbnail';
 } else {
      $theme_img = 'recent_works_iso_thumbnail';
 }

2.

if(isset($manta_option['iso_format_recent_works']) && 1 == $manta_option['iso_format_recent_works']){
    $theme_img = 'recent_works_thumbnail';
} else {
    $theme_img = 'recent_works_iso_thumbnail';
}

3.

if (!empty($manta_option['iso_format_recent_works']) && $manta_option['iso_format_recent_works'] == 1){
}
else{
}