string replace without using any in-built function - php

Question

With a program to replace substring in a string without using str_replace
should be generic function should work for below example:
Word : Hello world
Replace word : llo
Replace by : zz
Output should be: Hezz world
Word : Hello world
Replace word : o
Replace by : xx
Output should be: Hellxx wxxrld
This is what i wrote to solve it
function stringreplace($str, $stringtoreplace, $stringreplaceby){
$i=0;$add='';
while($str[$i] != ''){
$add .= $str[$i];
$j=0;$m=$i;$l=$i;$check=0;
if($str[$i] == $stringtoreplace[$j]){
while($stringtoreplace[$j] != ''){
if($str[$m] == $stringtoreplace[$j]){
$check++;
}
$j++;$m++;
}
if($check == strlen($stringtoreplace)){
$n=0;$sub='';
for($n=0;$n<=strlen($stringtoreplace);$n++){
$str[$l] = '';
$sub .= $str[$l];
$l++;
}
$add .= $stringreplaceby;
$i += $check;
}
}
$i++;
}//echo $add;exit;
return $add;
}
I am getting output as helzzworld .
Please take a look what I did wrong or if you have better solution for this please suggest.

Answer 1

You can do this by explode the main string into array then implode your stringreplaceby to your array parts creating new string
<?php
function stringreplce($str,$strreplace,$strreplaceby){
$str_array=explode($strreplace,$str);
$newstr=implode($strreplaceby,$str_array);
return $newstr;
}
echo stringreplce("Hello World","llo","zz")."<br>";
echo stringreplce("Hello World","Hel","zz")."<br>";
echo stringreplce("Hello World"," Wo","zz")."<br>";
echo stringreplce("Hello World","rl","zz")."<br>";
echo stringreplce("Hello World","ld","zz")."<br>";
?>

Answer 2

Try this simplest one, without using str_replace, Here we are using explode and implode and substr_count.
1. substr_count for counting and checking the existence of substring.
2. explode for exploding string into array on the basis of matched substring.
3. implode joining the string with replacement.
Try this code snippet here
<?php
ini_set('display_errors', 1);
$string="Hello world";
echo strReplace($string,"llo","zz");
echo strReplace($string,"o","xx");
function strReplace($string,$toReplace,$replacement)
{
if(substr_count($string, $toReplace))
{
$array=explode($toReplace,$string);
return implode($replacement, $array);
}
}
Solution 2:
Try this code snippet here not best, but working
<?php
ini_set('display_errors', 1);
$string="Hello world";
echo strReplace($string,"llo","zz");
echo strReplace($string,"o","xx");
function strReplace($string,$toReplace,$replacement)
{
while($indexArray=checkSubStringIndexes($toReplace,$string))
{
$stringArray= getChars($string);
$replaced=false;
$newString="";
foreach($stringArray as $key => $value)
{
if(!$replaced && in_array($key,$indexArray))
{
$newString=$newString.$replacement;
$replaced=true;
}
elseif(!in_array($key,$indexArray))
{
$newString=$newString.$value;
}
}
$string=$newString;
}
return $string;
}
function getLength($string)
{
$counter=0;
while(true)
{
if(isset($string[$counter]))
{
$counter++;
}
else
{
break;
}
}
return $counter;
}
function getChars($string)
{
$result=array();
$counter=0;
while(true)
{
if(isset($string[$counter]))
{
$result[]=$string[$counter];
$counter++;
}
else
{
break;
}
}
return $result;
}
function checkSubStringIndexes($toReplace,$string)
{
$counter=0;
$indexArray=array();
$newCounter=0;
$length= getLength($string);
$toReplacelength= getLength($toReplace);
$mainCharacters= getChars($string);
$toReplaceCharacters= getChars($toReplace);
for($x=0;$x<$length;$x++)
{
if($mainCharacters[$x]==$toReplaceCharacters[0])
{
for($y=0;$y<$toReplacelength;$y++)
{
if(isset($mainCharacters[$x+$y]) && $mainCharacters[$x+$y]==$toReplaceCharacters[$y])
{
$indexArray[]=$x+$y;
$newCounter++;
}
}
if($newCounter==$toReplacelength)
{
return $indexArray;
}
}
}
}

Answer 3

function ganti_kata($kata,$kata_awal,$kata_ganti){
$i =0; $hasil;
$panjang = strlen($kata);
while ($i < $panjang) {
if ($kata[$i] == $kata_awal) {
$hasil[$i] = $kata_ganti;
echo $hasil[$i];
}
else if ($kata[$i] !== $kata_awal){
$hasil[$i] = $kata[$i];
echo $hasil[$i];
}
$i++;
}
}
echo ganti_kata('Riowaldy Indrawan','a','x');
This code using php