制作数字格式？

Make format of number:

For example:
if number = 204433 output = 204K

if number = 84243
output = 84'243

if number = 8000 output = 8000

if number = 400 output = 400 How to formatted number to that's format?

I think you can try this

if(strlen($number) > 5) {
   echo substr($number,0,2).'K';
} elseif(strlen($number)) {
   echo numberformat($number,2,'.',"'"); // for example
} else {
   echo $number;
}

The number_format command can do what you are looking for.

string number_format ( float $number , int $decimals = 0 , string $dec_point = "." , string $thousands_sep = "," )

You wrote:

if number = 84243
output = 84'243

Example:

$in = 84243;
$out = number_format ( $in, 0, ".", "'");
// $out = "84'243"