How to fix Warning Illegal string offset in PHP

Magic word is: isset

Validate the entry:

if(isset($manta_option['iso_format_recent_works']) && $manta_option['iso_format_recent_works'] == 1){    $theme_img = 'recent_works_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{}

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';}