How to find ratio between two currencies at run time

[[Deleted]]

Hi,

I need to find the ratio between two currencies at run time. like below:

account_currency_ratio = slave_account_currency/master_account_currency ratio

it's simple if they're same or a Symbol exists which consists of these two currencies.

but I'm confused about how to find it if a currency pair doesn't exist consisting of these two currencies.

any hints please

b.t.w what is the list of currencies in which we can have account on MT4?

thanks and best regards,
Zeeshan