How to determine whether a letter is uppercase or lowercase in php

Method 1:

Use regular expression /^[a-z] $/ or /^[A-Z] $/ Make a judgment.

Examples are as follows:

 function checkcase($str)
{
             if(preg_match('/^[a-z]+$/', $str))
             {
                    echo '小写字母';
             }
             elseif(preg_match('/^[A-Z]+$/', $str))
             {
                    echo '大写字母';
             }
}

Related learning video sharing: php video tutorial

Method 2:

Use functions "ord()" and "strtoupper()" are used for judgment.

ord() The function returns the ASCII value of the first character in the string.

strtoupper() Function converts a string to uppercase.

Examples are as follows:

<?php
$str = &#39;a&#39;;
function checkcase1($str){
    $str =ord($str);
   if($str>64&&$str<91){
       echo &#39;大写字母&#39;;
       return;
    }
   if($str>96&&$str<123){
       echo &#39;小写字母&#39;;
       return;
    }
    echo&#39;不是字母&#39;;
}
function checkcase2($str){
   if(strtoupper($str)===$str){
       echo &#39;大写字母&#39;;
    }else{
       echo &#39;小写字母&#39;;
    }
}
echo checkcase1($str);
echo checkcase2($str);
?>

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