Ignore case sensitivity when comparing strings in PHP

I’m trying to compare words for equality, and the case [upper and lower] is irrelevant. However PHP does not seem to agree! Any ideas as to how to force PHP to ignore the case of words while comparing them?

$arr_query_words = ["hat","Cat","sAt","maT"];
for( $j= 0; $j < count($arr_query_words); $j++ ){
    $story_body = str_replace( 
        $arr_query_words[ $j ],
        '<span style=" background-color:yellow; ">' . $arr_query_words[ $j ] . '</span>',
        $story_body
   );
}

Is there a way to carry out the replace even if the case is different?

Answer

Use str_ireplace to perform a case-insensitive string replacement (str_ireplace is available from PHP 5):

$story_body = str_ireplace($arr_query_words[$j],
   '<span style=" background-color:yellow; ">'. $arr_query_words[$j]. '</span>',
    $story_body);

To case-insensitively compare strings, use strcasecmp:

<?php
$var1 = "Hello";
$var2 = "hello";
if (strcasecmp($var1, $var2) == 0) {
    echo '$var1 is equal to $var2 in a case-insensitive string comparison';
}
?>