PHP two-dimensional array, how to solve it

PHP two-dimensional array

$str = array (
“Network programming books”=>array(‘a’,’d’,’er’),
“Historical Books”=>array(‘boko’,’fd’,’popo’),
“Literature Books”=>array(‘fd’,’fd’,’fd’),
);

echo $str[0][2];

why not show

——Solution ———————
Of course not displayed! There is no subscript 0, how to display it?
——Solution ——————–
Because you originally The position of 0 is replaced by ‘Network Programming Books’
echo $str[‘Network Programming Books’][2]
——Solution —————– —
Your two-dimensional array, the outermost subscript of the associative array is a character, not a number
——Solution- ——————-
You can change the code to
$str = array (
array(‘a’,’d’,’er’),//Network programming books
array(‘boko’,’fd’,’popo’),//historical books
array(‘fd’,’fd’,’fd’),//literary books
);

echo $str[0][2];
This will show