problem with str_replace in an array in a loop

for ( $i = 0; $i <= count($keywordlist); $i += 1) {
$keywordlist[$i] = str_replace("X", "Y", $keywordlist[$i]);
}

PHP:

I cant seem to figure out why the above code doesnt work. I have echo statements after this bit to see if it worked, but when i use this code above the site just loads (for a bit longer than usual) and then i get NO output.

If i create a new array, lets say $testArray and use code like below, it works!

for ( $i = 0; $i <= count($keywordlist); $i += 1) {
$testArray[] = str_replace("X", "Y", $keywordlist[$i]);
}

PHP:

Now if i echo the components of $testArray, it works fine (notice however that i dont need assign a number for testArray, as it just appends the new string to the array). Why doesn't the code above (the very first code) work? I mean

$keywordlist[0] = str_replace("X", "Y", $keywordlist[0]

PHP:

works fine, so why won't it work if i use a variable ($i) in the for loop above?

Thanks!

 

why not doing this

$text = str_replace(array("from", "from1", "from2", "etc"), array("to", "to1", "to2", "toetc"), $text);

You can use arrays in str_replace

 

Thanks for your help, but I was trying to replace only one character in every string of my array, not do multiple replacements for a single string. for example, if these were the objects of my array:
"sampleX"
"textX"

i would want them changed to:
"sampleY"
"textY".

Simply changing all occurences of "X" to "Y" in every string of my array.