String Handling - Error with substr_replace

Question

I have a specific condition where I need to replace every instance of a "ct" with "c-t" provided there is a consonant before 'c' and a vowel after 't'. I am unable to do so :

<?php

$string = "october solatrix regnum sanctus sanctus";

echo constantCT($string);

function constantCT($string)
{
    $arr1 = str_split($string);
    $length = count($arr1);
    $pc=0;

    for($j=0;$j<$length;$j++)
        {
            $check = $arr1[$j+1].$arr1[$j+2];
            if($check=='ct')
                {
                    $pc++;
                }
        }

    function strAppend4($string)
    {
        $arr1 = str_split($string);
        $length = count($arr1);

        for($z=0;$z<$length;$z++)
            {
                $check = $arr1[$z+1].$arr1[$z+2];
                if($check == 'ct')
                    {
                        //echo "ct found <br>";
                        //echo $arr1[$z]; echo "<br>";
                        //echo $arr1[$z+3]; echo "<br>";
                        $verifyC = isConstant($arr1[$z]);
                        $verifyV = isVowel($arr1[$z+3]);

                        if($verifyV && $verifyC)
                            {
                                echo $z+2; 
                                $updatedString = substr_replace($string, "-", $z+2,0);
                                //echo $updatedString;
                                return $updatedString;
                            }
                    }
                else
                    {
                        //echo "ct not found <br>";
                    }
            }
    }

    $st1 = $string;
    for($k=0;$k<$pc;$k++)
        {
            $st1 = strAppend4($st1);
        }

    return $st1;

}

So I should get the output as :

october solatrix regnum sanc-tus sanc-tus

The ct in october should not be tampered with as before 'c' there is a vowel and not a consonant.

Answer 1

You can do this with a regex using character classes.

echo preg_replace('/([^aeiou]c)(t[aeiou])/', '$1-$2', 'october solatrix regnum sanctus sanctus');

PHP Demo: https://eval.in/659567

Regex101: https://regex101.com/r/Nqiaav/1

or with a stricter character class:

echo preg_replace('/([b-df-hj-np-tv-xz]c)(t[aeiouy])/', '$1-$2', 'october solatrix regnum sanctus sanctus');

https://regex101.com/r/Nqiaav/2 (can add/remove y if that isn't a vowel)

Also this assumes you only wanted lowercase, if you want to allow upper case as well use the i modifier, or add all capitals to the character classes.

Answer 2

Try this:

for($j=0;$j<strlen($string);$j++)
        {
            if($string[$j] == 'c' && $string[$j+1] == 't')
                {
                    substr_replace($string, '-', $j+1, 0);
                    $j += 2;
                }
        }
echo $string;