Show a number to two decimal places

What’s the correct way to round a PHP string to two decimal places?

$number = "520"; // It's a string from a database

$formatted_number = round_to_2dp($number);

echo $formatted_number;

The output should be 520.00;

How should the round_to_2dp() function definition be?

You can use number_format():

return number_format((float)$number, 2, '.', '');

Example:

$foo = "105";
echo number_format((float)$foo, 2, '.', '');  // Outputs -> 105.00

This function returns a string.