About the currency function on the opencart

currency:
set($currency):
Set the currency to be used in overall site.
public function set($currency) {
$this->code = $currency;
if ((!isset($this->session->data['currency'])) || ($this->session->data['currency'] != $currency)) {
$this->session->data['currency'] = $currency;
}
if ((!isset($this->request->cookie['currency'])) || ($this->request->cookie['currency'] != $currency)) {
setcookie('currency', $currency, time() + 60 * 60 * 24 * 30, '/', $this->request->server['HTTP_HOST']);
}
}
format($number, $currency = '', $value = '', $format = TRUE):

public function format($number, $currency = '', $value = '', $format = TRUE) {
if ($currency && $this->has($currency)) {
$symbol_left = $this->currencies[$currency]['symbol_left'];
$symbol_right = $this->currencies[$currency]['symbol_right'];
$decimal_place = $this->currencies[$currency]['decimal_place'];
} else {
$symbol_left = $this->currencies[$this->code]['symbol_left'];
$symbol_right = $this->currencies[$this->code]['symbol_right'];
$decimal_place = $this->currencies[$this->code]['decimal_place'];

$currency = $this->code;
}

if ($value) {
$value = $value;
} else {
$value = $this->currencies[$currency]['value'];
}

if ($value) {
$value = $number * $value;
} else {
$value = $number;
}

$string = '';

if (($symbol_left) && ($format)) {
$string .= $symbol_left;
}

if ($format) {
$decimal_point = $this->language->get('decimal_point');
} else {
$decimal_point = '.';
}

if ($format) {
$thousand_point = $this->language->get('thousand_point');
} else {
$thousand_point = '';
}

$string .= number_format(round($value, (int)$decimal_place), (int)$decimal_place, $decimal_point, $thousand_point);

if (($symbol_right) && ($format)) {
$string .= $symbol_right;
}

return $string;
}
convert($value, $from, $to):
Convert the given value from once currency to other. The parameters are $value means of what amount and $from means of which currency and $to mean to which currency is the value to be converted.
public function convert($value, $from, $to) {
if (isset($this->currencies[$from])) {
$from = $this->currencies[$from]['value'];
} else {
$from = 0;
}
if (isset($this->currencies[$to])) {
$to = $this->currencies[$to]['value'];
} else {
$to = 0;
}
return $value * ($to / $from);
}
getId():
Returns the currency ID.
public function getId() {
return $this->currencies[$this->code]['currency_id'];
}
getCode():
Returns the currency code.
public function getCode() {
return $this->code;
}
getValue($currency):
If the currency is set then returns the value nor it will return zero.
public function getValue($currency) {
if (isset($this->currencies[$currency])) {
return $this->currencies[$currency]['value'];
} else {
return 0;
}
}
has($currency):
Whether the request currency is available or not.
public function has($currency) {
return isset($this->currencies[$currency]);
}

currency converting function, currency library function, converting currency function in class of opencart